Searching for tool to predict voltage loss at GFI outlets

[sparrott4]

For low voltage lighting, electricians typically install one or more GFI outlets at outdoor locations near the 12V transformers. The lighting installer will design and install the system under the assumption that the GFI's will deliver the expected 120 volts.

It's sometimes the case, however, that the 120v side drops as much as 10v under the lighting load. Is there a tool or piece of equipment that can be used to predict voltage loss at the GFI under a set amperage load?

For example, an installer would know that his system will apply about 8 amps. He would take this tool, plug it into the GFI, dial it up to 8 amps, then measure the voltage. This would also help predict potential overloads at the breaker box.

Side question, if you see a big voltage drop at the GFI under reasonable loads, does that mean that the GFI was installed with under-rated wire (or daisy-chained wirring instead of pigtails with GFI's in series)? If so, any way to calculate that from load/voltage drop?

Thanks (and note, I'm not suggesting that non-electricians do any work on the 120v side, it would just be helpful for them to know when a GFI is suspect and to predict what voltage taps to use on the low voltage side).

 

[petersonra]

Re: Searching for tool to predict voltage loss at GFI outlet

Re: Searching for tool to predict voltage loss at GFI outlet

A better answer is probably to specify the maximum voltage drop you are willing to tolerate to the electrician before he installs the GFIs. He can up-size the conductors if necessary.

Keep in mind that just measuring the voltage at a specific point in time does not guarantee the voltage will stay the same. As the load increases in the rest of the house, it is not unusual for the voltage to vary. The utility power can vary substantially to as load increases.

The answer is that whatever precautions you take for the new wiring, there is no guarantee that the voltage drop from the old wiring or from the utility itself will not still cause the voltage to drop.

The electrician should have enough smarts to install enough new circuits for the landscape lighting so no overload occurs. I would not worry about that.

 

[al hildenbrand]

There are a number of "circuit analyzers" available on the market.

This Ideal SureTest unit is one possiblility.

Whether the electrician installs the low voltage lighting, or the do-it-yourselfer, neither is off the hook for responsibly adding load to an existing circuit, or even a new circuit. The laws of physics are remorseless.

The available voltage at the supply, the distance conductors must run to the 120 V receptacle, the current of the load of the new LV lighting, any existing load and its diversity already on the same circuit, ALL must be considered for a successful stable solution.

 

[Mike03a3]

There are a number of "circuit analyzers" available on the market.

This Ideal SureTest unit is one possiblility.

I have one myself and find it very useful, but it doesn't allow for "dialing in" a load to test the voltage drop. It has three fixed tests: 12, 16 & 20 amps.

Also - the price at the link provided is VERY high. I purchased mine for about half that at Ideal SureTest Circuit Analyzers

 

[celtic]

There are a number of "circuit analyzers" available on the market.

This Ideal SureTest unit is one possiblility.

I have one myself and find it very useful, but it doesn't allow for "dialing in" a load to test the voltage drop. It has three fixed tests: 12, 16 & 20 amps.

Also - the price at the link provided is VERY high. I purchased mine for about half that at Ideal SureTest Circuit Analyzers

They look like different models to me:
al hildenbrand's linked to

ES-164 @ $420

Mike03a3 linked to

or

61-164 @$220 ............................................................61-165 @ @265

 

[al hildenbrand]

Given the OP is coming from the perspective of a manufacturer. . .

All I did was Google "circuit analyzer" and take, I think it was, the third link. There's a wide world to explore. . .

I am neither endorsing nor recommending any particular product.

I assume the manufacturer will have an agenda that will inform the selections taken from the possibilities offered.

 

[hbiss]

Sounds to me like you are accusing a GFI receptacle of having something to do with voltage drop. The voltage drop across a GFI receptacle would be no more than any other receptacle of the same quality. Voltage drop will most likely be because of the wire feeding the receptacle or a problem with it.

it would just be helpful for them to know when a GFI is suspect and to predict what voltage taps to use on the low voltage side

You don't need to know anything more than how to use a cheap voltmeter. Wire everything up to the anticipated taps, turn it on, measure your voltages at strategic locations throughout the system then go back and adjust your taps accordingly. That is what must be done anyway just to balance the system and account for normal line voltage variations.

If your customers can't understand that basic concept then perhaps there is merit for requiring landscape lighting to be done by electricians.

-Hal

 

[celtic]

I am neither endorsing nor recommending any particular product.

That's not the answer I was looking for :? ...I'm looking to buy one of these testers and wanted an "endorsement"

 

[Mike03a3]

There are a number of "circuit analyzers" available on the market.

This Ideal SureTest unit is one possiblility.

I have one myself and find it very useful, but it doesn't allow for "dialing in" a load to test the voltage drop. It has three fixed tests: 12, 16 & 20 amps.

Also - the price at the link provided is VERY high. I purchased mine for about half that at Ideal SureTest Circuit Analyzers

They look like different models to me:
al hildenbrand's linked to

ES-164 @ $420

Mike03a3 linked to

or

61-164 @$220 ............................................................61-165 @ @265

No, same thing. Ideal doesn't have a p/n ES-164 on their site, and their pic of the 61-164 is the same one the first vendor used for the ES-164. It looks like mytoolstore is just using the pic from the previous model (61-154) which the -164 replaced. Here's the pic from Ideal for the 61-164:

I'm not pushing any vendor, I'm just pointing out the first price was way high. I've seen prices on electrical tools that vary dramatically. This is not an unusual example. caveat emptor

 

[Jljohnson]

While I understand your request for a meter to plug into the system, Mike also has a ver good voltage drop calculator in the form of an excel spreadsheet available in the "free stuff" section of this site. On a side note, from a EC's point of view, it is nearly impossible to determinre the loads for landscape lights at the time of circuit installations in my area simply because the plans will usually give you litle or no information about the systems that will be installed. Typical custom residence scenario goes something like this:
EC- Do you need any 120 volt stub-outs for landscape lighting or water features?
HO- I don't know, I hadn't thought of that yet. Just stub something out on the front and back of the house and we'll deal with it after we move in.

I recently did a 12,000 Sq. foot house where the homeowner replied just like that. We installed 6 dedicated 20 amp circuits around the perimeter of the home for future use. We just recently finished addind the additional circuits needed after the landscape was designe(Customer has lived in the house almost a year now). We added 2- three-phase 20 amp circuits(fed by phase converter/VFD combo's), 2-20 amp single phase 220 volt circuits, and 7 additional 20 amp circuits for landscape lighting. I know it's off-topic but sometimes my fingers won't stop typing.