Providing Electrical Power to your Grow


A Basic Guide to Electrical Terms, Calculations and Doing What You Can to Keep Things Safe 


Indoor grow rooms can use a fair amount of electricity. Here, we look at how to make sure you don't overload breakers, sockets or cables, and what you can do to make your grow room as safe as possible

A Guide to Electrical Terms and Equations

When it comes to mains electrical power terms there are really only 3 that it's essential to know about:

Voltage (V) - For mains electricity this will almost always be 230 Volts (in the UK).

Current (I) - Electrical current is measured in Amps and is a measurement of the amount of "flow" of electricity through something.

Watts (W) - Neither Voltage nor Current on their own are a measurement of how much electrical power something uses. Actual Power is measured in Watts (W).


There are other terms such as inductive load and resistive load, but most of the time the above 3 terms will cover it.


So, how do the 3 terms Above Relate to each other? - A Guide to Basic Electrical Equations

The simplest equation which uses the above 3 terms is Voltage x Current = Watts (or V x I = W or 230 x I = W).

This equation can be rearranged to find the current: Current = Watts ÷ Volts or (Current = Watts ÷ 230).

Please bear in mind that even if you have a 400V grow light, it still runs off a 230 Volt supply. The 230 Volts mains supply is converted into 400 Volts inside the ballast, so we still use 230 Volts for our Electrical feed calculations.


About Electrical Supplies

The limitations and specifications of an electrical circuit installation are almost always expressed in terms of how much current (Amps) that it can supply.

If you take a look at a domestic consumer unit you will usually find that the breaker for the ring mains (socket outlet) circuit is rated at 32 Amps and it there to protect the cables. The 32 Amps is the total for all the sockets in the installation. You must never pull 32 Amps from one mains socket outlet! That would be disastrous with overheating and fire likely to occur!

Each mains socket outlet face is only rated at 13 Amps. That applies whether it is a single or a double socket outlet. The total current that can be handled by a double socket outlet is still only 13 Amps, it is NOT 13 Amps through each side (i.e. it is NOT 2 x 13 = 26 Amps)!



Practicle Examples of Calculating Current Draw

For this example we're going to look at a grow light that uses 660 Watts of electricity. This could be a 600W HPS set to "Boost", or a Maxibright Daylight LED.

So using the equation above, Current = Watts ÷ Volts. So, in this case, Current = 660 ÷230. This means that the Current (I) = 2.87 Amps.

This means that each 660W Grow Light pulls 2.87 Amps, but how many of them can we run from one socket face?

As we already said, a socket face can safely supply 13 Amps. If we divide 13 by 2.87 we will get the number of lights that one socket face can run.

13 ÷ 2.87 = 4.53. We would round this down to 4 in order to stay under the safe limit of 13 Amps for any socket face. 4 x 2.87 = 11.5 Amps current draw in total.


Using Multi-Way Socket Strips

Now we ought look at how the power from the socket face is going to be split to go to the 4 lights.

Most growers will probably use a 4-way socket strip and this is where we need to be careful because not all socket strips are created the same.

Some 4-way socket strips can only handle 3 amps, some are rated at 6 amps, others are rated at 10 amps, but the best can handle a full 13 Amps like this one here.

If you are going to use a multi-way socket strip, you need to make sure it can handle what you are going to draw through it. In the case of 4 x 660w grow lights you would need one that can handle the full 13 Amps.


How Many Lights Can Be Run From One Mains Circuit? 

If we go a little bit further, we can calculate the total number of these lights that can be run from a standard domestic ring main circuit, as long as absolutely nothing else is being run on the circuit.

Well, as we said before, on a standard domestic ring main (socket) circuit, it is protected by a 32 Amp breaker on the consumer unit.

So, if we divide 32 by 2.87 we will find how many 660W grow lights can be run from that circuit.

32A ÷ 2.87A = 11.14 grow lights. Again we would round this down to 11, as long as nothing else is being run from that circuit anywhere in the building.

In the real world, a grower would be running extraction fans, circulation fans and probably a few other pieces of electrical equipment. The grow building may even be being lived in by a family with televisions, microwave ovens, kettles etc. being run from the same ring main circuit. This means that far fewer lights can actually be run from that circuit.

If you want to run more lights than that, or you have a lot of other equipment being run from the same socket circuit then you should seriously consider getting an electrician to install a separate circuit. This will involve putting an extra breaker into the consumer unit and appropriate cables being installed to carry the power to where it needs to go. 


Other Recommendations for Safety

As with all cabling from a mains socket, keep it neat and avoid creating trip hazards!

Also, make sure that no stress or strain is placed on cables or connections. Again, this can be a recipe for disaster.

Keep ballasts off the floor in case there is a flood. Water conducts electricity so the two do not mix well at all! Especially, keep ballasts off carpet as they can get very hot and could cause a fire. Ballasts are best placed at least on a wooden or metal platform off the floor. That way they will run a bit cooler which will probably make them last longer and helps to reduce the likelihood of a fire. We would strongly recommend using automatic fire extinguishers in case the worst should happen. They will help stop a small fire turning a house into a blaze!

Getting started