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Ask Erik: RAW! - Maximum Grow Lighting: How to Avoid Overload

Be careful trying to manage all that power, or you and your neighborhood could be in for a shock. Be careful trying to manage all that power, or you and your neighborhood could be in for a shock.


Hey, what do you recommend as the maximum number of lights I can run on a residential power service? I plant to run 1000 watt HPS lamps on digital ballasts.


That, my friend, is a can of worms! It’s going to depend on a number of factors, and the operative word should be how many lights can you run safely from your residential power service.

A lot of so-called experts tend to blow off this question and say “consult a qualified electrician.” While this is solid advice, and I also recommend you do so, let’s have a look at some of the things that are going to determine the answer to your question.

First, you need to know how much power you have coming into your residence; most places have either 100 AMP or 200 AMP services.

Secondly, are you planning on living in the residence - for example, are you going to use the oven or washer and dryer? If you are dedicating all available power to the grow, you can run a considerably higher number of lamps.

Thirdly, how are you going to be cooling your grow room, and what kind of set-up is it? If you are running a CEA (Controlled Environment Agriculture) or “sealed” room, you are going to need some serious air-conditioning power. Typically, this gobbles up about 30% of all of the power you have available for your grow, sometimes more. However, if you have access to large volumes of cold running water you might be able to use a heat exchanger instead, allowing you to create cold air without using lots of power. ust make sure that your water source is going to be cold enough, as some sources heat up in warmer months when you need the cooling power the most. It had better not run dry in mid-crop, either; that would spell disaster.

You absolutely MUST use a flip in doubling up on your lamps rather than installing a second set of ballasts.

Using air-cooled or water-cooled lamps greatly improves your cooling efficiency, allowing you to dedicate more power to grow lighting versus cooling. Mechanical vent fans, while noisy and offering less control over the environment, do use considerably less power to get the job done versus ACs.

In short, the “Surrey Rule of Thumb” is that you can run up to sixteen 1000W lamps in a residence that has a 100 AMP power supply, assuming you are dedicating all of that power to growing and not other appliances. This also gives you some allowance for cooling equipment and peripherals. If you are going to run a CEA environment that requires a heavy duty AC, reduce the number of 1000W lights to twelve.

Not enough? You can actually double those lamp numbers if you install a “Flip” system, where relays shift the load coming from the ballasts to another set of lamps. Basically, one ballast is running two lamps, just never at the same time. You absolutely MUST use a flip in doubling up on your lamps rather than installing a second set of ballasts. Otherwise, if all of the ballasts came on accidentally at the same time, you stand a very good chance of blowing the transformer outside of the residence (it can explode), essentially shorting out your ‘hood.

The neighbours will not be impressed, I assure you. Neither will your power service provider or the authorities. Have all of the wiring done by a qualified technician, and use certified components and parts for safety and peace of mind. Badly wired and over-loaded grows are unsafe to the community at large and give other growers, who do practice safety, a bad name. Don’t be that bad apple that ruins the whole barrel.

Don’t forget, you can always pay to have more power brought into the residence by your power provider. They are always happy to sell more power. In some areas, generators are an option too, but that’s a whole other story; they tend to use quite a bit of fuel, making it cost more to produce power than simply buying it from your electric company. Typically, generators are not kind to the environment either.

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You need to manage electricity in your indoor grow room.
Last modified on Monday, 08 October 2012 19:08

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