Neutral Problem?

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JoeNorm

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WA
Got a call from a customer who we just finished installing a "whole-house" battery backup. The system is about a week old and has performed normally until this evening.

The unit is such that the 200 amp feeders get routed directly to it, and it has an automatic transfer switch for when there is an outage. This is not our first install of the unit. It is a high quality unit.

Customer described flicking lights, smelling an electrical smell in the garage, and appliances acting weird.

We showed up and everything looked fine leading up to the main panel. Voltages were in the correct locations and correct values at the battery unit and at the main house panel.

Heating loads (240, no neutral) worked perfect. As we turned on 120 loads one by one, a voltage imbalance began to occur. Resistive loads like an electric kettle and toaster would not work at all. As we turned lights on one by one we heard a louder and louder humming noise coming from what appeared to be the large lugs in the battery unit where the utility lands. As the load grew, lights flickered more, as the humming noise intensified.

I am just wondering what those symptoms point to? A neutral problem apparently, but I have not seen enough of these problems to be able to recognize what is happening.

We were able to bypass the unit pretty easily but we'll have to return soon to figure out what is going on.

Thanks for your input in advance!
 
Did you check/record the voltages on each leg when the symptoms appeared? If not, you need to check neutral to hot on each leg when this is happening. Might even be good to have two meters, one for each leg.

Does this only happen when on back-up power?
Does the ATS switch the neutral as well?
 
Clearly neutral issues from your description. You should be able to find out where by measuring for a voltage difference across points in the neutral pathway where there should be no voltage differences.
 
I forgot to mention that I did check for loose connections in the unit, everything was rock solid.
 
Or point-to-point? If the incoming voltages are right, and the outgoing voltages are not, the problem must be within.

That means there will be a voltage, equal to half the imbalance, between the line neutral and the load neutral.

Check for both, my suggestion and for matching L-N voltages at each accessible point along the power pathway.
 
In normal conditions when the grid is present, the transfer switch is essentially passing the power straight through the unit. I was very surprised to find the problem was there, seeing as it is basically just a pass-through. If connections are correct and tight, hard to imagine what it could be.
 
JoeNorm said:
In normal conditions when the grid is present, the transfer switch is essentially passing the power straight through the unit. I was very surprised to find the problem was there, seeing as it is basically just a pass-through. If connections are correct and tight, hard to imagine what it could be.
Click to expand...

I've seen broken busses cause similar problems. The terminals are tight, but the issue is the buss is cracked.
 
JoeNorm said:
In normal conditions when the grid is present, the transfer switch is essentially passing the power straight through the unit. I was very surprised to find the problem was there, seeing as it is basically just a pass-through. If connections are correct and tight, hard to imagine what it could be.
Click to expand...
That's exactly why you need to do what we're suggesting. Make no assumptions. Check every point between parts.

There is a gap, electrically speaking, in the neutral pathway. You need to find it electrically, not visually or "wiggly".
 
Take your own resistive L-N loads to use when testing. Apparently you know where the problem is, or close to it. Take the time to use your meters, two are better, for some schooling. This is on your dime so make it worth the cost.

Put a L-N load on only one side. Check voltages L-N-L until you find the imbalance/balance. What is the VD across the suspect connection? What is the VD N-EG prior to and after this point?

Small Thermal scanners are less than $50. This would be a good place to play with one.
 
Are there tools made to put loads in various places or is that something homemade?

As I am not the owner of the company, this is not my personal dime, but I agree it's a good chance to learn.
 
JoeNorm said:
With alligator clips or something? Probes?
Click to expand...
As part of my test equipment I have made about two five foot lengths of cord with alligator clips on one end and 5-15 male on one and female on the other. In your case use the one with female end, clip on to whatever point you wish to apply load to and plug in whatever load you want - when I want to test a connection for weak connection 1000 watt + heat gun is usually my first load choice.
 
I agree with all the posts about the diagnostic measurements that need to be made.
Based on the symptoms I think the most likely problem area is:

1. The neutral conductor on the utility side and/or its connection to the battery backup unit, or
2. A defect inside the unit itself.

A bad neutral connection on the output side of the unit would effect the voltage voltage balance across L1-N and L2-N loads. But I don't think this would be distinguishable by the unit as a problem because it would just shift the load currents around somewhat.
The fact that the unit reacts by making humming noises in proportion to L-N loading could mean the neutral voltage on its input feed is shifting due to a bad connection somewhere on the utility side of the unit, and the internal electronics doesn't like that.

By the way, I assume the backup unit is located in the garage and that's likely why the customer mentioned an "electrical" smell in the garage?
 
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