Hydroponic Growroom Electrical Safety     


Note on Electrical Safety: Different voltage and safety standards exist in different locales. For example in the US, 120 volt is the standard with 220 volts for larger appliances and cable is measured in gauge. In Australia, 240 volts is the standard and cable is measured in mm. The following material discusses electrical standards (cable size, amperage ratings etc) in 240 volt situations.  Any electrical work should be conducted by a licensed professional and wiring should be compliant to safety standards within your locale.  


An extremely important issue that all indoor gardeners need to consider when designing and implementing their growroom is electrical safety. This is area of the utmost concern, but a factor that is far too commonly overlooked.


The reality is that a growroom, for lack of a better term, is an ‘industrial application’ which is configured using lighting and other equipment that was designed originally for industrial purposes. Many growers run a lot of HID lights which creates an extremely heavy power/amp/watt draw on electrical cables.   The problem is that most houses are wired for domestic, not industrial, purposes. This means that when a house is built, the wiring which is installed is done so with domestic purposes in mind. This often means that standard house wiring is inadequate for powering indoor grows.  Too often indoor growers fail to understand this and in some cases this ends in disaster.


For example, it is all too common to hear of house or shed fires as a result of indoor grows going up in flames.


A 2010 working paper from British Columbia notes a home with a grow operation is 24 times more likely to catch fire than a typical home.




“From 2004 to 2009, 314 fires across B.C. were caused by grow operations or drug labs, resulting in two deaths, 26 injuries and more than $16 million in damage.


From 2005 to 2009, 136 fires across B.C. were directly attributed to electrical bypasses and lights associated with hydroponic operations.”[1]


On this note:


  • Nothing will bring the emergency services to you house and your growroom like a fire. It doesn’t matter how stealth your grow is; if it catches fire, your grow will be found
  • Your house & contents insurance policy will not cover fire resulting from unlicensed electrical works in a room used to grow in. Further, if you have overloaded power points and/or extension leads beyond their designated maximum load your insurance company will not pay for damages.
  • Should your house or shed catch fire, your house will be subject to a costly electrical inspection and repairs/upgrades if any non-compliant wiring is found. Additionally, large fines will be incurred for any illegal wiring.
  • At best, should your house not burn down completely, a shed or house fire will undoubtedly result in eviction for renters and a compromised grow for home owners. In either instance, you lose a secure place to locate your grow when all of this could have been avoided.


Just one problem is that many growers set up their grow in a closet or a bedroom. They plug lights, fans, air conditioners and other high-load electrical devices into a wall outlet. However, in most cases the wall outlet is ill-equipped to handle the electrical load. There are several things that can be problematic. The wiring and/or the outlet might be old, damaged, frayed, shorted, or otherwise compromised. The circuit box and breaker that supports the outlet may be inadequate to handle the increased electrical load. Most wall outlets are rated at 10 amps. A single 1000 watt magnetic/coil ballast draws 4.2 amps at 240 volts, so by plugging two 1000 watt HID lights into a wall outlet in locales that use 240 volts this would mean you were drawing 8.4 amps giving you plenty of room for safety right?


Not really!


One very important factor that is too commonly overlooked is that safety amp (electrical load) ratings for power outlets and cable are calculated for short term use only. That is, it is important to note that most household circuits (typically 15 amps at 240 volts in Australia) can safely handle 95 – 100% of their max rating, but only for an hour or so at a time. Loads that require long periods of ‘on’ time (like HID lighting) should not exceed 80% of the max rated load of the wire/cable and wall outlets. Given that grow rooms run HID lighting for long periods of time (i.e. 18 hours on and 6 off in grow or 12/12 in bloom) any electrical considerations should factor in that the wiring to the growroom and any power outlets should only be subjected to 80% of the stated maximum load. This means that a 10 amp GPO powering HID lighting for 12 to 18 hours at a time suddenly becomes an 8 amp outlet. In understanding this we can quickly establish that a single standard household GPO, in electrical safety terms, is inadequate for grow rooms that run even a couple of 1000 watt lights.


Where 600-watt lamps are concerned, a quality 240 volt, 600-watt digital ballast such as Lumatek draws a stated 2.7 amps, so technically you’d max out a wall outlet with 3 x 600-watt digital ballasts (8.1 amps).


Then there is the actual cable that runs from a power circuit of your house electrical board to your growroom. Most modern houses in Australia are wired using 2.5mm cable to GPOs (general power outlets). 2.5mm cable is rated to carry a maximum load of 27 amps. However, this rating is halved to 13.5 amps when the cable is surrounded by thermal insulation and is inside a wall, which pretty much describes most house wiring situations. Also, remember that ratings are established for short-term use only. We therefore want to only use 80% of the stated maximum safety rating which leaves us with 10.8 amps on a standard house wiring 2.5mm cable which is surrounded by thermal insulation and is inside a wall. That’s not a lot of amps right? This perhaps tells you that if you are planning on running more than a few HID lights you need to consider your growroom wiring carefully.


Besides the risk of fire, the risk of electrocution due to substandard wiring is an ever-present danger. Electricity is deadly stuff. You can’t see it, you can’t smell it, but it can very easily kill you when things go wrong.


Hydroponic grows include lots of electricity and water in close proximity. Water is an extremely good conductor. Where water comes into contact with live electrical equipment, it can carry the electricity to areas it was not intended to go. This includes you. It is all too easy to become the earth for faulty or wet electrical equipment. Anyone who has experienced a high amperage electrical shock and lived to talk about it will tell you this is something you definitely want to avoid.


Fires can also be caused electrically through what is called leakage current. Leakage current occurs when water is in the presence of electricity. Exposed wiring, which exists primarily at connectors and switches, can come in contact with water. Since water conducts electricity, a current will flow through the water between contacts or from the live to ground or common. Over time, the water will accumulate salts which increase its ability to conduct a current. This current can eventually develop to a point where it generates a significant quantity of heat which begins to pyrolize and carbonize the combustibles in the area. This can result in a situation where a carbon bridge is formed, creating a continuous arc or significant generation of heat. Ignition of surrounding combustibles can result in fire.


Because water and electricity do not play nicely together it is critical that electrical equipment is kept away from water and high humidity, and no matter what your grow room (and you!) are protected by a ground fault circuit interrupter. A ground fault circuit interrupter (GFCI) also referred to as a Ground Fault Interrupter (GFI) or Residual Current Device (RCD), acts as life-saving device which is designed to prevent you from getting a fatal electric shock if you touch something live, such as a bare wire. It can also provide some protection against electrical fires.


GFCIs measure the current on the current-carrying conductors and detect any leakage. Leakage could be current leaking through your body or the chassis of an HID ballast.


There are different kinds of GFCI breakers. Some are built to protect equipment and most (any available for residential & light commercial usage) are built to protect people from electrocution. The GFCI’s manufactured for our protection trip at about 5/1000th of an amp (5mA). This means that should you become the ground for a piece of electrical equipment, while you may get a tingle, the shock isn’t nearly enough to kill you (currents between 100 and 200 mA are deemed lethal).


The most modern type of circuit breaker is a combination safety switch and circuit breaker called a residual current circuit breaker with over current protection (RCBO). RCBOs protect single circuits from shorts, overloads and electric shocks. Essentially, RCBOs are overload circuits which also offer protection from fatal electric shock, and which protect a single line wired to them.


Besides a GFCI or RCBO, another piece of electrical safety equipment that every grow room must have is a smoke detector. Keep in mind that many growers run their lights at night when they are asleep. Should a fire start during this time, the smoke detector may just save your home and/or your life by alarming you that there is a fire in the grow room.  You should also have a fire extinguisher on hand. These are best left outside of the grow room because if there is a fire inside the room you may not be able to safely access the extinguisher. These days you can purchased automated fire extinguishers (e.g. Flame Defender) for less than a couple of hundred dollars. These units detect high temperatures (generally around 92oC/199oF) and activate automatically when the temperature indicates a fire is present.


Resistance and Voltage Drop 


Electrical cable that is overloaded will result in voltage drop which is not only dangerous but can result in damage to electrical equipment. I.e. electrical current is the flow of electrons through a substance that will permit that flow. The substance is called a conductor. For example, an electrical wire is a conductor so electrical wires and things like extension leads are conductors. Some conductors are better than others, but none are perfect, and all resist electron flow to some extent. When electron flow is resisted, some of the energy in the electrons does not travel through all the way. Because energy is conserved, the energy that is moving the electrons forward is converted to heat. If too much heat is created, eventually the insulation around the wires may begin to melt but this is not obvious; it may just be a small portion between the copper wires inside. As this happens more and more current begins to flow between the wires and eventually this causes a fire.


Voltage drop occurs because voltage drop of a circuit is in direct proportion to the resistance of the conductor and the magnitude of the current. If you increase the length of a conductor, you increase its resistance. The longer your wire/cable is from the electrical ‘in’ point to the outlet, the potentially lower the voltage is at the point of utilization. Another key factor that influences the amount of resistance, besides length, is wire size because the larger the cross sectional area of a wire, the lower the resistance, since the electrons have a larger area to flow through. Therefore, a 6mm wire will have less resistance than a 2.5mm wire. Think of this as wire being a highway for electricity.  The more lanes you have, the faster the cars go through, where the number of lanes represent the wire thickness and the cars represent electrons. When electrical resistance is too high this causes traffic to slow because there are too many electrons trying to pass through too small a cable. As a result, voltage drop occurs.


When severe voltage drop occurs, the results is the inconvenience of having your hydroponic electrical equipment shut down intermittently, which damages your equipment and interrupts the orderly provision of light, water and other factors to your plants. In less severe cases voltage drop can slowly damage your electrical equipment causing it to eventually fail. This means, besides the risk of fire due to overheated cabling, voltage drop can be a costly problem (electrical gear fails/becomes damaged and you are forced to replace it).


Electrical Equipment with Safety in Mind


There are electrical power timer boxes available through hydroponic stores which come with RCBOs, timers which switch on electrical contactors’ and multiple plugs/sockets/outlets which run from these contactors’ with a given number of outlets being protected from overload via the RCBO.


Electrical contactors are electromagnetic switches that are designed to carry heavy electrical loads. A contactor works as a switch when the coil is energized or de energized. Contactors, among other things, protect low amperage rated electrical hardware such as timers, from electrical overload. For example, a timer, if wired without a contactor, can be subject to a heavy amp draw by things such as HID ballasts. This can eventually damage the timer. Where that timer is wired to a contactor, it simply switches on the contactor which takes the heavy amp draw of the HID ballasts, protecting the timer from overload. I.e. the contactor acts as a buffer between the ballasts and the timer, taking the electrical load off the timer.


Electrical timer boxes are configured to be hard wired in to a dedicated line (single phase) or three lines (three phase) and they are supplied with a 10mm (or larger) live and neutral wire along with ‘blue point’ electrical connectors (insulated caps into which wires are placed and joined) onto which growers can hardwire from the mains board electrical wiring which runs from a dedicated circuit.  They’re extremely nice pieces of equipment; configured to modern electrical safety standards and a must have for any grower who is running more than a few lights.  Additionally, the beauty of these boxes is they have been wired by licensed electrical engineers and, therefore, act as extremely safe plug and play power supplies/outlets for HID lighting and other grow room equipment. Dependent on your electrical requirements (number and wattage of ballasts/lights etc) there are boxes configured to handle most situations.


HID Lamps Emit a Lot of Heat – Lamp Security is Imperative


HID lights emit a great deal of heat and therefore they need to be considered as a fire risk factor in any growroom.


Stories abound in the grow culture of where HID lights exploding or falling from their mounting positions have caused a near miss, or worse, a growroom fire.


Hang your lights securely to ensure they stay safely anchored above your crop (and not on it).


Exhaust Fans 


When you first start indoor growing the setup cost can seem exorbitant. Initially you can save a few dollars buying some cheaper equipment and perhaps go back to things and upgrade later when you have a bit more cash. However, there is some equipment where it is ill-advised to purchase cheaper options.


For example, stories abound in the grow culture of exhaust fans failing, creating excessive, sometimes dangerous, room temperatures. This not only creates a fire hazard but also, more often than not, results in significant yield losses, if not catastrophic crop failure. This situation generally comes down to ‘thermal cutoff’ switches turning off fans leaving the grow room without exhaust.


A thermal cutoff is an electrical safety device that interrupts electric current when heated to a specific temperature. These switches are incorporated into fans for motor overheat protection and therefore are a critical safety feature of any fan. I.e. they stop fan motors from overheating and catching fire. It’s a bit of a catch 22 situation; the thermal cutoff is incorporated into fans to prevent fires. If the thermal cutoff is faulty it may fail and the fan motor might overheat causing a fire risk. However, if the thermal cutoff shuts down the exhaust in the grow room this too increases the risk of fire (the environment gets super-heated) while also probably ending in plant stress or, worse, plant death.


Just one problem is that some fans aren’t suited to the relatively high temperatures they may be working under in indoor grow environments. So, for example, if a fans thermal cutoff is set to cut off at too low a temperature along comes hot weather and BLAM (oh no!), the all-important exhaust fan goes down.


In other instances, it isn’t unheard of that cheaply produced fans have faulty cutoffs which shut down the fan at any given temperature (take your pick). Then again, a faulty cutoff may not be working at all causing the fan to overheat, creating a fire danger.


Ultimately, the thermal cutoff is a critical part of both airflow efficiency and electrical security/fire safety. Additionally, it is a critical part of ensuring your grow room remains adequately cooled through exhaust. Therefore, this single little electronic component can mean the difference between optimum yields or catastrophic crop failure.


Thermal Cutoffs and Fan Quality


The thermal cutoff temperature – the deemed to be safe operating temperature of a fan – is determined by the quality of that fan.  That is, a quality fan is designed and constructed with a maximum safe operating temperature in mind. Therefore, a suitable cutoff temperature is determined by factors such as the material the fan casing is produced from, the quality of the motor, the circuitry and wiring etc. A quality fan which is suitable for indoor growing will have a casing that is manufactured from either metal or a robust poly casing that can handle high temperatures (i.e. the casing is fire/bullet proof), a motor that is extremely reliable and robust, and componentry (circuits, thermal cutoff, wiring etc) to match.


This said, it is not unheard of that some manufacturers copy high quality e.g. German fans and produce them in e.g. China. The only problem is that the original product may have a metal or a robust high-quality poly casing and incorporate state of the art, bullet proof German produced componentry while the Chinese product is produced using low grade plastic and cheaper, less robust and reliable components. Just one of these less reliable components may be the thermal cutoff.


In other cases you even hear of thermal cutoffs being removed completely in cheaply produced fans. For example, in one recent case one manufacturer/supplier of a Chinese made fan decided to remove the thermal cutoffs after they received complaints that their fans were switching off resulting in more than a few super-heated grow rooms and no doubt more than a few less than happy customers. The problem is (to stress the point) thermal cutoffs are a safety feature built into fans to ensure they don’t overheat and catch fire. Inasmuch, this manufacturer/supplier had just illegally modified their product to not only make them non-compliant to electrical safety standards but they had also made their fans a potential grow room fire hazard. I cover a lot more on electrical/fire safety later in the book.


Suffice to say, for now and for what it is worth, exhaust fans are one piece of equipment where it is advised to spend a few extra dollars from the outset.


When selecting an exhaust fan, ask your retailer where is the fan produced? Is it a high quality German or Swiss motor? Or is it a Chinese motor? The latter may indicate an inferior product! Look on the box to see where the fan is produced. Just because a fan brand has a European sounding name doesn’t mean it was made in Europe or some other country that indicates high-quality production standards. Do some research online about the fan brand you are considering purchasing. Maybe post a thread on a forum and ask other growers about their experiences with the fan.


Price is also a good indicator. High-quality fans tend to cost a bit more at point of sale than inferior products. It’s a sad fact of life, but you typically you get what you pay for. Pay little and you might just be purchasing problems which cost you a lot more than that extra 50 to 100 dollars for a quality fan at point of sale. Pay a bit extra initially and you may just save yourself and your plants a lot of problems later.


Using Extension Leads/Cords in Your Growroom


Technically speaking, extension leads are designed for temporary use and not for permanent installation. For this reason, growrooms are ideally hardwired for the purpose.


This said, in practicality, many growers choose to use at least some extension leads in the grow room. For example, when considering electrical timer boxes that are purchased through hydroponic stores, these boxes are isolated to one point of the room with all the power outlets feeding out to HID ballasts etc located at this point. This means that if ballasts and other electrical equipment are positioned some way away from the timer box, extension leads are required.


For this reason, let’s go through some safety issues/tips that will make this practice as safe as possible.


Some Safety Rules for Extension Cords


  • Keep extension leads out of the way of foot traffic

If you absolutely must use extension cords for long periods of time make sure they are completely out of the way and not subject to physical damage via foot traffic. If the internal metal wires of an extension lead are damaged, such as by the cord being crushed in a door or squashed by foot traffic, then where the unbroken part of the wires is narrower than the bulk of the wires, this can form a point of high resistance. A hot spot may develop as the resistance of the narrower part of the wire is higher than the rest of the wire, and thus tends to concentrate power dissipation and heat there. Get extension leads off the floor and out of the way so that they don’t become tripping/safety hazards and can’t be damaged by foot traffic.


Where extension leads are used, do not run extension cords through walls or ceilings. This may cause the cord to overheat, creating a fire hazard. Do not nail or staple electrical cords to walls or baseboards. Make sure that cords are not pinched in doors, windows, or under heavy equipment, which could damage the cord’s insulation.


Never place extension leads under carpet or rugs (or anything else) as they may overheat.


  • Keeps leads short and to the length required

Every meter of lead increases the electrical resistance, in turn decreasing the power the cord can deliver and creating more heat. Therefore, the longer the cord, the larger the diameter of the conductors need be to minimise voltage drop. Because of this, it is best to use a cord that’s exactly as long as needed and no more.


  • Uncoil extension leads/cords fully


Current flowing in a cable generates heat. This causes the temperature of the conductor/wire to rise. If the temperature gets too high the insulation on the cable softens and eventually melts.


When you pack lots of cables that are all carrying current (whether multiple separate cables or multiple loops of the same cable) together heat dissipation suffers resulting in a higher temperature at a given current.


The normal cable ratings of extension leads assume that the wire can adequately disperse heat generated in the cable due to the current flowing.


If a lead is coiled up and using close to the maximum rating it increases the chance of melting the plastic insulation and then causing a short.


For this reason it is important to fully uncoil extension leads.


  • Bunched cables must be de-rated for current carrying capacity


If you are running multiple extension leads which as close to one another (e.g. all running along a line on top of each other) maximum amp ratings need to be downgraded. In a situation like this I would typically only run the extension lead at 50% capacity (i.e. a 10 amp rated cable would be down-rated to 5 amps).


  • Poor electrical contacts cause fires


Poor electrical contacts create heat. When plugs are not plugged in all the way there is less contact, which reduces cross-sectional area of the contact and heat is generated. Electrical plugs must be pushed in all the way into wall outlets (GPOs) as well as extension cords. If the plug fitting feels lose then this fitting is unsafe.


  • Allow a large amperage safety margin


The fact is that extension leads are cheap so why take the risk of overloading them?


General purpose household extension leads are made using 1.5mm wire and are rated for 10 amps. With the 80% safety margin where running power through the lead for long periods of time this leaves us with 8 amps.


However, for safety reasons it is highly recommended that you only use 80% of the 8 amps. This leaves us with 6.4 amps.


For myself, I only ever run 1 x 600 watt 2.7 amp ballast per standard household extension lead. This costs me a few bucks more than running say two ballasts through an extension lead but gives me peace of mind in knowing that my leads are safely under their maximum electrical load (by a mile).


Multi-Outlet Power Boards 


Power boards can turn a single electrical outlet, which can only hold one or two plugs, into one that can accommodate multiple plugs. While this sounds ideal it can be extremely dangerous if you overload the power board. This said, for reasons of practicality many growers do use multi-outlet power boards in their grow room. For this reason, let’s look at some safety rules if and when you choose to use multi-outlet power boards.


  • You should NOT run high wattage appliances (such as HID lights) through power boards. For this reason avoid the use of multi- outlet power boards for running HID lights and/or other high load electrical equipment.
  • Use power boards with overload and surge protection. This will prevent the board from overheating.
  • Only use power boards with built in safety switches/circuit breakers
  • Regularly check that all plugs are firmly fixed in power boards
  • Regularly check the power board for any signs of damage and degradation
  • Always ensure your power-boards are kept clean and dust free, as built up dust over time can enter the socket outlet and cause a fire.
  • Allow a large max amp safety margin. For example, if a board is rated to safely carry 10 amps, down-rate it to 5 amps (half)
  • Never loop power boards (i.e. plug one board on to another) and avoid the use of double adapters on boards.




[1] Ensuring the Safe Installation of Hydroponics Equipment – A Discussion Paper, 2010. Fire Chiefs Association of British Columbia

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