GB Electrical Receptacle Tester & Circuit Analyzer GRT500A

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Quick and Easy

Apr 21, 2003 (Updated Apr 21, 2003)
Review by  
Rated a Very Helpful Review

Pros:Could not be easier to use

Cons:Doesn't test for ground faults

The Bottom Line: This is a fast and simple tool to check if your electrical outlets are properly wired.


I've done a lot of electrical work in my homes over the years and have a lot of respect for the power of electricity. It is amazing stuff when properly distributed and used, but it can turn on you in a flash if something is incorrectly installed.

When I bought an older house a few years ago, I got a GB GRT-500A receptacle tester to make sure all the outlets were wired properly. For a cost of less than $10, I found two outlets in the house that were incorrectly wired – knowledge that may very well have prevented a painful shock… or worse.

The GB GRT-500A receptacle tester is a little yellow plastic thing that looks like a grounded electrical plug with delusions of grandeur. The device is a little bigger than a standard plug and it is fitted with three lights that glow in various combinations when you plug it into an outlet. It does require that you have grounded outlets; you can't use the GRT-500A with one of those three-prong adapters.

On its case is a chart that shows various electrical circuit conditions and the unit can be used with no trouble regardless of whether your outlets are installed with the ground hole up or down. Obviously, since it has the three prongs of a grounded plug, the GB GRT-500A will go into a receptacle in only one way.

Using it could not be easier… simply plug it into a grounded receptacle. If all is well, one of the lights will light up indicating that the receptacle is properly wired and everything is normal. Depending on the pattern of lights that illuminate, the GB GRT-500A can also indicate the following circuit flaws:

-Open ground
-Open neutral
-Open hot
-Hot/ground reverse
-Hot/neutral reverse

One of these – the "open hot" indication – indicates a condition that is probably not dangerous. The other four fault conditions are something to be worried about and one – "hot/neutral reverse" – is particularly dangerous, although the others could be surprising if you’re not paying attention.

To explain this, let me discuss a little about home wiring. Almost all homes in the US (and probably Canada) are wired from the power company for 240 Volts. The 240 Volt circuit is split in half (at the pole) with a device called a transformer, and the home is fed with two 120 Volt circuits and a neutral wire. The two 120 Volt circuits are 180 degrees out of phase, so if you measure from one circuit to the other you will get 240 Volts. Measuring from either circuit to the neutral wire will give you 120 Volts.

The outlets in your home are fed by one or the other of these two 120 Volt circuits, passing through your circuit breaker panel and distributed around the home. Each outlet gets a hot wire (with 120 Volts on it), a neutral wire (with zero Volts on it) and a ground wire (also with zero Volts). The hot wire is almost always covered in black insulation, although it sometimes has red insulation. The neutral wire is always white and the ground wire is either bare copper or covered in green insulation.

Many older appliances – especially older TV and stereos – had the neutral wire attached to the metal chassis of the appliance. This is okay if it is, in fact, the neutral wire. But if someone has mis-wired the outlet, you could now have 120 Volts on the chassis. Although the appliance will probably work just fine, this is a tragedy waiting to happen if two such chassis happen to be touched at the same time.

Modern appliances usually run the hot wire to the on/off switch first, and the neutral wire is allowed to contact the circuitry in the device. If the hot and neutral wires are switched, this puts live voltage into the circuitry of the device, even if the on/off switch is off. Meanwhile, the chassis is connected to the ground wire. Somebody examining this appliance could be in for a painful surprise.

In any event, one five-second check with the GB GRT-500A will tell you if the hot and neutral wires have been switched. This is VERY cheap insurance.

I have not had the GRT-500A trip a GFCI (ground-fault circuit interrupter) breaker when I’ve plugged it in. Which brings up another point… the GRT-500A does not test for GFCI operation. This means that you can plug the unit into a bathroom GFCI outlet and it could read that everything is normal, even if there was a problem with the GFCI function in the outlet.

To test for GFCI function, GB has the GFI-501A tester that is very similar to the GRT-500A but includes GFCI testing capability. It wasn’t available when I bought my GRT-500A or I might have paid a bit more for the GFCI capability.

(If anyone wants me to add a description of how a GFCI works, let me know and I will add it. In case you are wondering, GFCI is also known as GFI… these two terms mean the same thing.)

I have bought three more homes since I first got my GRT-500A and I have used it to test all the outlets when I examined the new homes. In two of these cases, I found incorrectly wired outlets, which I used as leverage to get the home price down.

Although I feel very comfortable fixing this problem, you may want to call a qualified electrician. If you don’t know which end of a screwdriver is used to hammer a nail, you really should call an electrician before tackling this problem.

The GB GRT-500A receptacle tester is a very handy and durable device for checking that your electrical outlets are properly wired. Considering that improper wiring is an invitation to a nasty shock or even an early death, it is an essential item for almost any household. It is really necessary if you are buying an older home that was wired 30 or more years ago, but mistakes are made today and there could be an accident waiting to happen in your brand-new home.

For less than $10, the GB GRT-500A receptacle tester is easy to use and gives you a lot of peace of mind. But if I were in the market today, I would probably get its big brother, the GFI-501A, which can test GFCI operation.


Recommend this product? Yes

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