Power surge at customer's home

[Nutmegger]

Sorry, a little long of a write-up, but it's a good mystery if you like them:

The boss man sent me to this house to install an in-panel surge suppressor that the homeowner requested.
When I came to the place, this is what the h/o told me:

Apparently, there was a power surge that fried some appliances about a week ago.
It happened on a bright, clear day - no winds, no rain or lightning.
The neighbors did not have any issues (the h/o went around and asked), although one of them said that his whole-house generator kicked in.
Here is the aftermath:
Two surge strips in the house burned up - they both smoked, but the connected TV, cable box and other misc. electronics survived.
The fridge stopped working.
I was thinking, maybe it's a bad neutral, but probably not; The line-to-line loads were affected, too: The 240V A/C compressor blew up. The starting capacitor exploded, and after replacing the capacitor, the a/c guy told the h/o that there is a lot more damage than that.

The homeowner filed a complaint with the POCO, so they said "we don't know" and then came in and installed a power monitor into his meter socket. It's still there.

The service is an underground lateral from a pad transformer on the side of the road stubbing up into a meter on the side of the house.
It's a 200A service.
Just for the heck of it, I put my clamp around phase 1 and 2 - both read roughly around 3A.
The neutral, however, read 2A (shouldn't it have been close to a zero?). Tried again and again, to make sure some other load didn't kick in while I was repositioning the clamp - same result.
The current on the neutral went to zero when I opened the main breaker, which is probably a point against the bad utility neutral theory.
The L1 and L2 to neutral showed 120 volts give or take. The L1 to L2 showed 235 volts (again, strange). My clamp multimeter is a decent Klein model - never had any accuracy issues with it.
Nothing on the surface shows any present issues with the service.
Nothing else strange happened again since the apparent surge (1 week ago) - no lights flickering or any other appliances burning up, even though they had winds and rain since then.

I told the h/o to wait with his surge suppressor until the POCO is done with the monitoring, and asked him to let me know what they say (if they say anything at all, of course - it seems to be against their interest to fess up to something at this point).

At this point this is strictly academic - I am curious more for my own knowledge, since the h/o is duking it out with the POCO.
I did not share any of my own theories with him (not that I have any).
Any other thoughts as to what could have happened on that clear sunny day?
Why is the neutral current 2A higher than the sum of the L1+L2 while the main breaker is on?

 

[hbiss]

Why is the neutral current 2A higher than the sum of the L1+L2 while the main breaker is on?

There can be circulating currents from neighboring properties if they share the POCO neutral and the water system. But if the current goes away when you open the main I would suspect a neutral problem someplace.

As to the surge, obviously had to be a primary to secondary cross someplace in POCO territory. Really not much to debate there.

-Hal

 

[Hv&Lv]

Couple of things..
When checking the neutral where were you checking it?
Opening the main and the current went to 0 just means the power was off while you were checking..
It in itself doesn’t really point to the poco.
Leave the breaker on and check the POCO neutral in the meter box on the POCO side, but make sure the ground rod and water connections aren’t behind the clamp on meter. This will tell you if the currents are flowing through the water bond, cablevision ground, to the ground rod, etc.. if it’s everywhere except the POCO neutral with nothing behind it but the XF, now there is probably an issue on the POCO side.
who knows.. it could be a loose neutral connection on the meter box at one of the lugs there..
Point is if your calling the poco make sure you are past all customer owned connections.

If you can take a hairdryer or a large 120V space heater and connect it to one lug at the top of the main. Turn it on and check voltage. I’ve seen them fail to come on when you turn it on because the neutral shows itself with this imbalance.
you want a large 120V load to off balance the transformer and load the neutral.
Do it with the heater rather than the customers microwave..

I’ve been with a POCO for 30+ years. Don’t wait for a confession. Show them.

 

[Fred B]

You stated a neighbor's whole house gen came on about same period of time? Is that neighbor on the same pad mount transformer as your customer? Any other neighbor also? If the house with the gen and your customer are the only ones on the transformer there maybe a relation for the incident. If the gen set installed incorrectly and bonding incorrectly done a surge may have occurred. Unlikely if there was no outage, the gen may have only started in a scheduled exercise mode, and wouldn't actually throw any current out, and it would have presented before unless it is a brand new install.

You state you turned off the main and current went away on the neutral, did you follow up by turning off all the individual branch breakers? Including the double pole 240V? Results? Were all the damages that you relate on same leg of system? HVAC tech mentions a lot of other damages to AC, maybe that initiated the other damages if all damages on same leg.

What was your boss's response to you're not selling the surge after he sent you to do that? I would not be happy, especially if you came back with no plausible reason with definative documentation for the surge such as open neutrals, or other actual or suggested repairs. Installing the load side surge protection shouldn't effect the POCO monitoring.

 

[electrofelon]

Why is the neutral current 2A higher than the sum of the L1+L2 while the main breaker is on?

Could well just be meter error. I question the accuracy of cheap clamp meters for low single digit measurements

 

[Nutmegger]

I measured the currents before the main breaker lugs for the hots and before the neutral/ground busbars main lug for the neutral. There are no ground connections at the meter socket - the water bonding connection and the GEC are at the panel.
I checked with the "mother ship" before NOT installing the surge suppressor - the h/o did not tell us about the power monitor at the meter.

BTW, the POCO tech was the one who originally pointed out the 2A "excess" current on the neutral when he was installing the power monitor, but he did not have any explanation for it. I wish I was there when he came, but it sounds like he's just a guy who goes around pulling and installing meters and related meter socket equipment.

I tried running a space heater on both legs, and did not notice any voltage drop.

I am interested to know whether (or how) the A/C compressor failing cascaded into an overvoltage event for the whole house.

 

[Nutmegger]

You stated a neighbor's whole house gen came on about same period of time? Is that neighbor on the same pad mount transformer as your customer? Any other neighbor also? If the house with the gen and your customer are the only ones on the transformer there maybe a relation for the incident. If the gen set installed incorrectly and bonding incorrectly done a surge may have occurred. Unlikely if there was no outage, the gen may have only started in a scheduled exercise mode, and wouldn't actually throw any current out, and it would have presented before unless it is a brand new install.

You state you turned off the main and current went away on the neutral, did you follow up by turning off all the individual branch breakers? Including the double pole 240V? Results? Were all the damages that you relate on same leg of system? HVAC tech mentions a lot of other damages to AC, maybe that initiated the other damages if all damages on same leg.

What was your boss's response to you're not selling the surge after he sent you to do that? I would not be happy, especially if you came back with no plausible reason with definative documentation for the surge such as open neutrals, or other actual or suggested repairs. Installing the load side surge protection shouldn't effect the POCO monitoring.

Fred, thanks bud.
It's a sparsely populated area, so there are not that many neighbors around. With the genny - my theory was that it has a power quality monitor, and when sensing over- or under-voltage it kicks in.
When you say on the same leg - the line-to-neutral loads suffered on both legs, and there was damage to the line-to-line loads (A/C compressor).
The boss did not know about the power monitor and agreed with my decision to let the dust settle with the POCO and their monitoring equipment.
Can you tell me more about how the A/C compressor failure could have caused the damage? I see the capacitor "firing back" into the wiring of the house causing a spike, but it's hard to believe that this does not happen more often?

 

[synchro]

Just for the heck of it, I put my clamp around phase 1 and 2 - both read roughly around 3A.
The neutral, however, read 2A (shouldn't it have been close to a zero?). Tried again and again, to make sure some other load didn't kick in while I was repositioning the clamp - same result.
The current on the neutral went to zero when I opened the main breaker, which is probably a point against the bad utility neutral theory.

The neutral current could be from the power factor on the L-N loads.
For example, let the L1-N load be 3A with PF = 0.777 (from a motor, for example), and the L2-N load be 3A with PF = 1.0 (a resistive load).
Then arccos(0.777) ≈ 39.0 degrees. Therefore the L1-N and L2-N currents are 180 - 39.0 = 141.0 degrees apart. The components of the L1-N and L2-N currents that are in phase with each other will appear on the neutral, and each will contribute 3A x cos( (180°- 39.0°)/2 ) = 3A x 0.3338 ≈ 1.00A. Therefore the total neutral current will be 2 x 1.00A = 2.00A

 

[Hv&Lv]

The neutral current could be from the power factor on the L-N loads.
For example, let the L1-N load be 3A with PF = 0.777 (from a motor, for example), and the L2-N load be 3A with PF = 1.0 (a resistive load).
Then arccos(0.777) ≈ 39.0 degrees. Therefore the L1-N and L2-N currents are 180 - 39.0 = 141.0 degrees apart. The components of the L1-N and L2-N currents that are in phase with each other will appear on the neutral, and each will contribute 3A x cos( (180°- 39.0°)/2 ) = 3A x 0.3338 ≈ 1.00A. Therefore the total neutral current will be 2 x 1.00A = 2.00A

I don’t know many home appliances these days that are that bad. 45degrees in a home is pretty bad and would(should) trigger some kVar metering.

 

[synchro]

I don’t know many home appliances these days that are that bad. 45degrees in a home is pretty bad and would(should) trigger some kVar metering.

In the example I gave kVAR = 120V x 3A x sin(39°) ≈ 0.23.
Capacitor run and PSC motors would have a better power factor, but capacitor start and split phase motors would typically have a power factor significantly less that 0.78, particularly at light loading. Some of those are still out there.