Double-pole breaker not tripping

rguimond · Mar 26, 2019

I apologize in advance if this is off-topic, but I really need to understand what's going on...

While doing some renovations, it was found necessary to relocate a few runs on BX (aluminum-sheathed) cable. One of the cables ran between a single-pole thermostat and a 240V baseboard heater. After trying unsuccessfully to locate the breaker, I turned up the thermostat to ensure both hot lines were energized and cut through it (while wearing arc-flash protection, or course), with an old set of linesman's pliers.

Guess what? The breaker didn't trip! I stripped off a few inches of aluminum sheathing and bared the ends of both hot conductors. When I touch them to the ground conductor, there is only a very small spark and the breaker DOESN"T TRIP, even after holding it for several seconds.

I confirmed that there is 118 VAC in reference to ground on both hot conductors. Interestingly, there is ZERO potential between the hots, which leads be to think the circuit was improperly connected from the time it wa installed and that the baseboard heater never worked. Regardless of this oversight by the installer, this should not cause a breaker to fail to open.

Definitely a top-ten entry in my weirdest encounter.

Any suggestions, guys?

Rob... · Mar 26, 2019

There isn't enough fault current to trip the circuit breaker, what rating and type (B,C) etc...

How long is the cable run?

Have you actually verified the ground connection.

In the UK we call it an earth loop impedance test. I know it's not commonly done in the US so not sure if it is in Canada either.

5618 · Mar 26, 2019

Federal Pacific breakers? If so, they're junk. Replace the panel. There's much information online about them.

rdrast · Mar 26, 2019

Sheesh... Don't play games like just shorting things out to find a breaker. In the event of a faulty breaker, you are more likely to just burn the place down.

Go get a Fox and Hound to start with, or some other live wire tracer, but the F&H works well.

Next, shorting one phase to ground may or may not show current flow, it depends how the upstream side of the supply is connected. There would be a fault current if there is a neutral bond to ground, on the same supply (no other isolation), but if the electrical system was installed poorly, I wouldn't count on proper neutral bonding, or proper ground continuity anywhere.

tragically1969 · Mar 26, 2019

rguimond said:
I apologize in advance if this is off-topic, but I really need to understand what's going on...

While doing some renovations, it was found necessary to relocate a few runs on BX (aluminum-sheathed) cable. One of the cables ran between a single-pole thermostat and a 240V baseboard heater. After trying unsuccessfully to locate the breaker, I turned up the thermostat to ensure both hot lines were energized and cut through it (while wearing arc-flash protection, or course), with an old set of linesman's pliers.

Guess what? The breaker didn't trip! I stripped off a few inches of aluminum sheathing and bared the ends of both hot conductors. When I touch them to the ground conductor, there is only a very small spark and the breaker DOESN"T TRIP, even after holding it for several seconds.

I confirmed that there is 118 VAC in reference to ground on both hot conductors. Interestingly, there is ZERO potential between the hots, which leads be to think the circuit was improperly connected from the time it wa installed and that the baseboard heater never worked. Regardless of this oversight by the installer, this should not cause a breaker to fail to open.

Definitely a top-ten entry in my weirdest encounter.

Any suggestions, guys?

Holy s**t, is it April 1st already ? I can't believe what i am reading, is this really the best you could come up with for fault finding ??????

Anybody seen playing that game in the UK would find themselves without a job pretty quickly.

rguimond · Mar 26, 2019

I have a contractor on it. I'm in the hospital following major stomach surgery. It just so happened that the surgery was scheduled for the evening this mess was detected.

The notion to verify the ground actually cam to me just after I recovered.

The distribution panel in Siemens. Installed in 2015

I'll update once I'm able to contact the site

cardosocea · Mar 26, 2019

rguimond said:
I apologize in advance if this is off-topic, but I really need to understand what's going on...

While doing some renovations, it was found necessary to relocate a few runs on BX (aluminum-sheathed) cable. One of the cables ran between a single-pole thermostat and a 240V baseboard heater. After trying unsuccessfully to locate the breaker, I turned up the thermostat to ensure both hot lines were energized and cut through it (while wearing arc-flash protection, or course), with an old set of linesman's pliers.

Guess what? The breaker didn't trip! I stripped off a few inches of aluminum sheathing and bared the ends of both hot conductors. When I touch them to the ground conductor, there is only a very small spark and the breaker DOESN"T TRIP, even after holding it for several seconds.

I confirmed that there is 118 VAC in reference to ground on both hot conductors. Interestingly, there is ZERO potential between the hots, which leads be to think the circuit was improperly connected from the time it wa installed and that the baseboard heater never worked. Regardless of this oversight by the installer, this should not cause a breaker to fail to open.

Definitely a top-ten entry in my weirdest encounter.

Any suggestions, guys?

Do you have that many breakers that would take you longer to trip one at a time to see which is feeding this heater?

Reading what you wrote, it seems you cut the thermostat wires. Is that what you've done?

Does your home have a transformer? I thought Canada's distribution was 120Vac.

sbaum · Mar 26, 2019

rguimond said:
One of the cables ran between a single-pole thermostat and a 240V baseboard heater. After trying unsuccessfully to locate the breaker, I turned up the thermostat to ensure both hot lines were energized and cut through it (while wearing arc-flash protection, or course), with an old set of linesman's pliers.

Guess what? The breaker didn't trip! I stripped off a few inches of aluminum sheathing and bared the ends of both hot conductors. When I touch them to the ground conductor, there is only a very small spark and the breaker DOESN"T TRIP, even after holding it for several seconds.

Any suggestions, guys?

It appears this is a single 2 conductor cable going to the thermostat? If so this is merely a 'switch-leg' in one line of the heater circuit. This is a very common method. When you touch the 2 conductors, it is just closing the switch circuit.

Now granted, you do have a ground problem. My guess is the ground wire in the heater is loose and needs to be tightened. So having that contractor come on over is a great idea.

But next time... maybe don't use the brute force method with cutting a wire.

Aabeck · Mar 26, 2019

Since there is only a small spark it might be improperly tied into another unit. You would still get the potential but the current would go through 2 things (heaters?) Since the current is going through the other unit there might not be a short circuit to trip a breaker.

Also, since there is 0V between hot leads it obviously is wired wrong to start.

You will have to get the Fox and Hound that Rdast linked to to find out where the power is wired from, and through.

shooter · Mar 26, 2019

is the system grounded at any point, when using separation transformers this would be the solution.

rguimond · Mar 26, 2019

Aabeck said:
Since there is only a small spark it might be improperly tied into another unit. You would still get the potential but the current would go through 2 things (heaters?) Since the current is going through the other unit there might not be a short circuit to trip a breaker.

Also, since there is 0V between hot leads it obviously is wired wrong to start.

You will have to get the Fox and Hound that Rdast linked to to find out where the power is wired from, and through.

It's not a switch leg. The thermostat junction bx is fed directly from the distribution panel. Only on heater on the circuit

jraef · Mar 26, 2019

Since we have to guess, my guess is that this was a DIY hack job done by someone who didn't know what they were doing, and they used a "twin" breaker as if it were a two pole breaker. that doesn't work because on a twin, both poles are connected to the SAME leg of the 240V lines. So there is zero potential between them. Given the improper connection to the hots, it's highly likely that the original installer didn't connect the ground correctly either.

And yes, that would have meant your heater never worked, unless said nincompoop rigged the heater to go to ground at it's connection box, in which case it was a 240V heater (illegally) getting 120V and would have been giving out a lot less than rated heat. In fact come to think of it, that might explain the "low spark of high heeled boys" you experienced, because that would put the heating element(s) in SERIES with your supposed short circuit test.

Leukic · Mar 27, 2019

wonder if both hots are coming from the same leg?

rguimond · Mar 29, 2019

jraef said:
Since we have to guess, my guess is that this was a DIY hack job done by someone who didn't know what they were doing, and they used a "twin" breaker as if it were a two pole breaker. that doesn't work because on a twin, both poles are connected to the SAME leg of the 240V lines. So there is zero potential between them. Given the improper connection to the hots, it's highly likely that the original installer didn't connect the ground correctly either.

And yes, that would have meant your heater never worked, unless said nincompoop rigged the heater to go to ground at it's connection box, in which case it was a 240V heater (illegally) getting 120V and would have been giving out a lot less than rated heat. In fact come to think of it, that might explain the "low spark of high heeled boys" you experienced, because that would put the heating element(s) in SERIES with your supposed short circuit test.

That's what I was thinking, too, but there are no "twin" breakers in the panel.

This was an installation done by professionals on a new plant in 2015. I only started in late 2017, so I don't have the advantage of knowing exactly who performed the work or what quality-control checks were done post-installation.

The service to the plant is 1500A 600V 3-phase. This panel servicing the heaters is fed from a step-down transformer with 600V primary. I'm still not back onsite, so I can't confirm if it's a 120/240 or 120/208, but it shouldnt matter

rguimond · Mar 29, 2019

Leukic said:
wonder if both hots are coming from the same leg?

I would guess that this is the case, but the breaker should still have tripped

Double-pole breaker not tripping

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