Loaded Voltage Drop

[tonype]

Just got a new receptacle tester (Sure Test) that performs some things other than reversed polarity, etc. and testing of the GFCI's. It tests for loaded voltage drop (LVD). I get the idea, but am trying to fully understand what causes a high LVD to occur.

From my understanding, LVD's in excess of 5% of considered substandard. Today I had a relatively new home (5 years old) that had readings as much as 17% with the line voltage reading 99 volts. Stuff in the panel was very professionally installed and all breakers protected properly sized conductors. So I am somewhat perplexed.

Is this condition due to poor connections along the way - say at the receptacle? Are there other causes?

 

[Nium]

What were the voltage readings at the panel on the service cable? How big of a house because if it's big enough could be the receptacles are more then 100 linear feet of wire away from the panel. Otherwise you maybe right that there is some issue at the respective receptacle(s) causing an increase in resistance.

 

[tonype]

What were the voltage readings at the panel on the service cable? How big of a house because if it's big enough could be the receptacles are more then 100 linear feet of wire away from the panel. Otherwise you maybe right that there is some issue at the respective receptacle(s) causing an increase in resistance.

House was about 2600 sq. ft. Some of the worst reading were the ones furthest away; however, this was not always the case (one circuit was in the basement family room within 30 feet of the panel - closest to the panel - no more than 10 feet away - had about a 6% drop and then increased to about 11% furthest away).

 

[kwired]

As mentioned before you need to check the voltage at the service also, could be a problem ahead of the branch circuit your'e testing. Size of service conductors, distance to transformer, size of transformer, number of other customers supplied by that transformer and conductors can all contribute to the problem.

 

[bob]

Tony
Check and determine how much load you tester is putting on the circuit. From some information I've seen, these tester load the circuit far in excess to what is normal.

 

[Nium]

I just spent a little time reading up on the Ideal Sure Test models 61-164 and 61-165 they do seem like useful testers but it looks like it could be easy to read them improperly. It maybe a good idea to follow the calibration and test procedures to make sure the tester is working correctly. Looking at the Ideal website the url for the Performance Test page is...

http://www.idealindustries.com/media/pdfs/products/manuals/61-160_series_technical_manual.pdf

If you had already followed the Performance Test procedures then try using a different multimeter/voltmeter to verify voltage at the service then at the respective receptacles to verify the readings from the Sure Test.

It just seems odd to have such low readings in a house that's not that big, nor that old (relatively speaking) 99 volts at a 17% drop would mean the service would be 115.83 VAC which seems low even for the service voltage.

 

[Jim W in Tampa]

Many things cause voltage drops. Problem could be several adding up to this. Back stab devices are never good. You might have bad connections at panel. Size of wire for long runs. The amount of wire is hard to see after drywall. Your device might be 300 feet if house is large and if the electrician ran #14 you could have a serious voltage drop. I would start by putting a heavy load on the house , turn electric heat on,dryer, range with all burners, etc . Get the load up to 50 or even 100 amps per leg and see what you have at the service. POCO are allowed to be low, not sure of number but 110 /220 would be ok. If you then add your other drops you just might hit 99 volts.

 

[SG-1]

Could there be other loads on the circuit under test that you are not aware of ?

Plug a multimeter into the other recepticle and watch the voltage there while performing the test. By measuring between the ungrounded conductor & the EGC you can see the voltage at the panel, provided the circuit is correctly wired. By measuring between the grounded conductor & the EGC you can see the volt drop. By measuring between the ungrounded conductor and the grounded conductor you see the voltage at the load.

 

[tonype]

As a home inspector, I do not have the ability to do many of these items. I am just going to red flag my concerns and refer my clients to a licensed electrical contractor for more detailed performance testing.

 

[SG-1]

Let me correct an error in my previous post. The reading between the ungrounded conductor & the EGC is the voltage at the panel before the load is applied. After the test starts the difference in the reading is the volt drop on the ungrounded conductor only as the EGC is not carring any current. This could help to determine which conductor may have a high resistance connection.