Random Trips when HVAC kicks on

[synchro]

... For all of the 20A circuits I just used dual function AFCI/GFCI breakers. When the hvac kicks on it trips 1-5 random breakers, and 1-5 more every time it cycles. If all are reset at night by morning almost every 20A breaker will have been tripped.

So I went back to this jobsite this past Saturday. Spent 4-5 hours troubleshooting and narrowed it down to a breaker. It has passed final inspections and I can't get support from the hvac company or installer, so I swapped it for a standard 20A single pole. Problem solved...
Now for the fun stuff. This one breaker would trip and cause another one or three around it to trip ONLY when the heat would kick on. ...
... I'd already moved 20A breakers around to see if they'd trip in another slot, but it still was random, but I had one more that I hadn't moved yet after all that and it happened to halt the issues.

So when this one dual function breaker tripped it would cause some other ones to trip. But after it was already tripped it could somehow still make even more dual function breakers trip when the heat was cycled back ON again? Just trying to understand what might be happening here.

 

[StarCat]

I think most of us would like to know the ’whys’ but we can’t afford to investigate continually at our own expense. Telling that to the customer who sees items we installed ’fail’ repeatedly is a PR nightmare.

This is correct, and is also because so many Tradesmen at large keep accepting and tolerating Bad Engineering and a continual devolution of systems that once worked perfectly with relay logic even. The forces that are driving these trends, aside from being monetized are not good ones.
The HVAC install sounds like a hack job, and sadly this is the case across not just that one trade in many instances.The control transformer connection says that all the work that outfit does likely follows this same pattern, or worse. This is a time when being old school is a strict advantage because it allows for a proper understanding of what actually works compared to all the snake oil systems that are being sold to people who do nto know any better and think they are getting something modern and supposedly high tech.

 

[Baxter83]

So when this one dual function breaker tripped it would cause some other ones to trip. But after it was already tripped it could somehow still make even more dual function breakers trip when the heat was cycled back ON again? Just trying to understand what might be happening here.

Yes, that is the phenomenon

 

[ptonsparky]

You need to find the common denominator. The breaker itself is not it. The conductors to it and the relationship to the others, maybe. Shared neutrals. Their proximity to one another.

I didn't go back to check, but have you tried a panel mount surge suppressor yet?

 

[synchro]

So when this one dual function breaker tripped it would cause some other ones to trip. But after it was already tripped it could somehow still make even more dual function breakers trip when the heat was cycled back ON again? Just trying to understand what might be happening here.

Yes, that is the phenomenon

This is a WAG, but perhaps it's just the electronics within the problematic breaker that was causing false trips on other breakers. There might be an instability or oscillation in the electronics that's triggered by a transient or interference produced when the HVAC turns on. In the ~ 10-100 kHz range often used for detecting arc faults the L-N impedance at the panel bus could be quite a bit higher than at 60 Hz because of the inductance of the service conductors, etc. And so such oscillation energy might be readily transfered through the panel busses over to the other dual function breakers, which then causes at least some of them to trip. Just throwing this out there. Without the right equipment and measurements there'd be no way to really tell whether this was happening.

 

[hbiss]

This is a WAG, but perhaps it's just the electronics within the problematic breaker that was causing false trips on other breakers.

This is why you replace the breakers first.

-Hal

 

[Eddie702]

Sounds like the HVAC guy hacked something up. Was the little transfomer added ? or original?

You said the fan motor was ramping up. Sounds like an ECM motor

 

[Baxter83]

 

[hbiss]

Why is everything 20A? This commercial?

I would make them change that transformer to one with a 240V primary. It might not be causing a problem now but it is a violation to use the ground to supply power for anything. And if you had breakers supplying that unit that had GFCI functionality they would surely trip.

-Hal

 

[ptonsparky]

That transformer sure looks added to me. HVAC clustered something.

 

[ptonsparky]

Is that the SE? If so, where is the bonding screw? I don’t use SQD to speak of.

NM, I went back to 1st post & see it’s a sub.

 

[g-and-h_electric]

Hal:

I saw the same thing with how that transformer is connected..... Aside from the code violation, It could be (IS ?) throwing an objectionable current on the ground (Fng HACK HVAC techs... our shop would prolly fire a guy for doing that .... boss says either use the right part or dont finish till you do!) . This could be the problem....

My first thought as a test only, would be to power the transformer from a 120 volt circuit with a piece of cord (isolating the primary from the HVAC power), and see if that solves any problems... I by some chance it does, Then a new transformer with a 208/ 240 primary should fix everything.


Howard

 

[ptonsparky]

A new transformer may help but it's still an add on that shouldn't be there.

 

[Baxter83]

Hal:

I saw the same thing with how that transformer is connected..... Aside from the code violation, It could be (IS ?) throwing an objectionable current on the ground (Fng HACK HVAC techs... our shop would prolly fire a guy for doing that .... boss says either use the right part or dont finish till you do!) . This could be the problem....

My first thought as a test only, would be to power the transformer from a 120 volt circuit with a piece of cord (isolating the primary from the HVAC power), and see if that solves any problems... I by some chance it does, Then a new transformer with a 208/ 240 primary should fix everything.


Howard

I thought it was, but even with the xformer isolated completely tripping if and around the breaker (top left missing in the picture) still occured. Yes, questionable things going on in this air handler. I'm not impressed.

 

[Baxter83]

Is that the SE? If so, where is the bonding screw? I don’t use SQD to speak of.

NM, I went back to 1st post & see it’s a sub.

It's a subpanel. The main disconnect is outside.

 

[Baxter83]

Hal:

I saw the same thing with how that transformer is connected..... Aside from the code violation, It could be (IS ?) throwing an objectionable current on the ground (Fng HACK HVAC techs... our shop would prolly fire a guy for doing that .... boss says either use the right part or dont finish till you do!) . This could be the problem....

My first thought as a test only, would be to power the transformer from a 120 volt circuit with a piece of cord (isolating the primary from the HVAC power), and see if that solves any problems... I by some chance it does, Then a new transformer with a 208/ 240 primary should fix everything.


Howard

I know the owner of the hvac company and plan to have a word (friendly, of course) about this xformer issue and suggest a 240P so that he's not using G as a conducter.

 

[hbiss]

I seriously doubt that the transformer is your problem but it absolutely needs to be replaced with the proper one.

From your saying that you hear the fan "ramp up", it would indicate a VFD which are notorious for messing with AFCIs and GFCIs.

-Hal

 

[Baxter83]

I seriously doubt that the transformer is your problem but it absolutely needs to be replaced with the proper one.

From your saying that you hear the fan "ramp up", it would indicate a VFD which are notorious for messing with AFCIs and GFCIs.

-Hal

Correct. The transformer wasn't the cause because the problem continued repeating with it totally disconnected.

About the vfd, this is the conclusion that I keep coming to.

 

[Baxter83]

Why is everything 20A? This commercial?

I would make them change that transformer to one with a 240V primary. It might not be causing a problem now but it is a violation to use the ground to supply power for anything. And if you had breakers supplying that unit that had GFCI functionality they would surely trip.

-Hal

Just saw this one. No, it's residential. It's a pretty big house on one story, so I chose to use all 12-2 because of the length of the runs. 14 age would probably have sufficed and been just fine, but I prefer to underutilized the higher ampacity cable than the other way around.

I'm planning to call him (the hvac guy) on this one, but need to wordsmith it in a way not to pi$$ him off that I got into this brand new unit

 

[Gilwell]

Are there Variable Speed Drive motors in any of the HVAC equipment; compressor(s), blowers? If so, you could be experiencing Harmonic Distortion - particularly at inrush - that confuses the microprocessors in AFCIs in the same distribution system and results in false/nuisance trips.