Q: My house was built in 1932 and only has two prong outlets. Can I still run growlights?

A: All growlights that come from reputable manufacturers (like Sunlight Supply) have three prong plugs.
The extra prong is a safety ground.

All hardware stores in the USA will be happy to sell you an adapter.

Q: OK, so will the two prong to three prong adapter add a ground somehow?

A: Well, maybe, sometimes.

Q: You're not exactly going out on a limb here.

A: We have been wiring houses for AC electricity about 90 years, now. During that time, we have learned a thing or two.
We started out with a system called "knob and tube". In this system, the key to safety was to keep the wires insulated--or really--to keep the wires from touching each other by using ceramic pieces that will not conduct electricity.
There was one wire coated with a black insulated coating (usually a rubberized cloth) that carried the "power" and another wire coated with white that was the return wire, called the "neutral". The wires were held about four to six inches apart by attaching ceramic insulators to the rafters, wall studs, or floor joists. These ceramic "knobs" fastened to the wood and also held the wire away from the wood and each other. Whenever the wires needed to go through a wall or stud, etc. a hole was drilled, and a ceramic tube was inserted in the hole, then one of the wires was pulled through. This system is generally pretty safe as long as the wires aren't touched over the years by adding attic insulation on top of them, remodeling, adding metal pipes that touch them, etc.

After that, we used plastic coated wires for insulation that were pulled through metal pipes which were then called "conduit".
The metal pipes connected to metal boxes, inside of these boxes all the wire connections were made. The metal conduit and metal boxes formed a connection themselves where the metal touches metal that would conduct any stray electricity back to ground. This was the first big use of a "safety ground". The wire colors stayed the same: black for power, white for neutral, return. The metal conduit itself, could catch any stray electrons and channel them safely back to ground.
The adapter from the hardware store is made for a system like this where the tang on the adapter is connected to the screw which holds the cover plate on the outlet (or "plug-in"). The screw on the cover plate on the outlet is connected to a piece of metal on the outlet itself; the metal on the outlet is connected to the metal mounting box that holds the outlet; the metal box is connected to the metal conduit; the conduit is connected to the breaker box or fuse box--which is grounded.
After that, we decided it was a lot simpler to just run an extra ground wire. This safety ground wire is coated with green insulating plastic. Different areas of the country have different code standards. Some places required an extra ground wire inside the metal conduit, some did not. Some places that required an extra safety ground wire required the wire to be bare with no insulation, some required the green coated wire. Wiring in commercial buildings requires this metal conduit with a coated ground wire inside in most communities today. Some residential wiring that goes outside the building has this same requirement. (Check your local codes.)
For residential wiring, we then went to the double insulated and grounded Romex wire that we talked about on the previous page. The ground wire allowed the use of lower cost plastic boxes and plastic conduit.

N.B. In some states it is illegal for you to touch the wiring--even if you own it and the house--if you have not served a union apprenticeship. Since these basic theories are covered in a 9th grade Science class the fact that it may be illegal in your state perhaps says more about local politics and the local educational system than about safety. Your local hardware store may get into trouble for giving you advice; you may have to drive to another nearby state.






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These pages are for information only--check your local codes or hire qualified service workers before doing any work. Make sure all work is done safely.