Is short-circuiting a good way to test if a breaker is safe?

Question

I am looking at the electrics in a house that a friend just bought, and it has one of the problematic "Stablok" Federal Pacific panels. Watching this video, made by a supposed master electrician who I find to generally be pretty good:

https://www.youtube.com/watch?v=tX-Ze8KhN10&t=540s

He talks about ways to determine if a Federal Pacific panel is really dangerous. This includes pulling the breakers to look for signs of overheating damage to the breakers and/or the bus bars.

But the part that gave me pause was where he talks about testing the actual breakers, to see if they trip properly when shorted. He first says to turn off a breaker, then short neutral to hot somewhere on the circuit, and then see if the breaker allows itself to be turned back on; seems reasonable. He then talks about shorting neutral to hot on a live circuit, disclaiming that you shouldn't try this unless you're very experienced.

I'm curious was the wiser people here think of these suggestions. To me, shorting a live circuit is crazy, mainly because you could cause overheating and/or wiring damage somewhere else (perhaps hidden) in the circuit, and never know it. Seems like even the technique of shorting a dead circuit and seeing if you can turn the breaker on, is suspect if you do it using the circuits conductors in the house - for the same reason.

But what about this? Turn off a breaker, disconnect its hot lead, and run a short jumper from the hot terminal to the neutral bar; then see if the breaker will turn on. This eliminates the possibility of doing any damage to installed wiring.

Answer 1

Let me start by saying after replacing failed stablock/ Federated(FPE) panels in the US, I will not work on them with the exception of replacement.

Now you are considering creating a short on a breaker type known to cause catastrophic failures and have the panel go up in smoke. I would think about that first. Not only do the breakers fail to trip or open with an over current event, the “stab” design is also a failure point. Messing with a stablock panel is not wise, even for a pro. After they are replaced, the connection can still fail. This is why the design was abandoned.

I became very anti stablock after work both failure’s and service calls.

For grins I actually tested several panels worth (not the panels that burned up) with no visible damage. Quite a few of these breakers did not open at 500% until they started smoking (I was using a breaker test bed)

To your question

Have I ever shorted a line to test? Well yes I have a plug in unit that basically dose this and I would never use it on an FPE panel using the homes wiring, it could trip late after overheating the insulation and later finish off the job with a fire.

My professional opinion is it was irresponsible and foolish to create the video, but there are all kinds of Youtube videos on how to do almost anyything, safe or not. There were supposedly videos on eating tide pods, which I would also not recommend.

Really I would not do anything with a stablock other than recommended replacement.

Answer 2

He first says to turn off a breaker, then short neutral to ground somewhere on the circuit, and then see if the breaker allows itself to be turned back on; seems reasonable.

This not reasonable. It is a waste of time. We don't put overcurrent protection on neutral, so the breaker won't notice anything different.

If the breaker were a GFCI, it should trip that but using a purpose-built GFCI tester that leaks just enough current to ground to trip the GFCI (~6mA) is a far safer way to test a GFCI.

It would also detect reversed polarity - the breaker should trip if the white wire you shorted to ground was actually hot. But again, there are much safer ways to go about this - like a voltmeter or a lightbulb and a known-good neutral/ground reference.

But what about this? Turn off a breaker, disconnect its hot lead, and run a short jumper from the hot terminal to the neutral bar; then see if the breaker will turn on. This eliminates the possibility of doing any damage to installed wiring.

This is a very bad idea. FPE breakers are known to jam on overload. You might be able to turn the breaker on and then not turn it off due to the defective FPE design.

But wait, there's more! There's a good chance the panel is either a "rule of six" panel with no main breaker, or whatever main it has between the meter and the breaker you're testing is also FPE and affected by the same "jams on overload" condition. Now you've got a piece of wire burning up in your panel with no way to turn it off.

FPE busses and breakers are fatally flawed. This is a settled topic. They should be replaced as soon as possible. Even if they seem to work today, that doesn't mean they won't fail tomorrow.

Leave the experimentation to the professionals. Don't listen to YouTubers.

Answer 3

Besides the other excellent answers here, there's another way of thinking about this situation, which is that: Sometimes, empirical tests are a great way to learn things or solve problems, while other times, empirical tests are a really, really bad way.

I'm not an electrical engineer, but I work with them and one thing that drives me insane is when someone designs a circuit where a component is used slightly outside of its specification in some way. There's always some "good reason" for this (usually it's because no part with specifications meeting the circuit's crazy requirements is available), but it sets you up for miserable, frustrating, preventable disasters. Sometimes the circuit works — because you "get lucky" and the component in question magically performs properly outside its specification — and sometimes you don't. But circuits that randomly don't work are the worst! I've even heard of organizations that try to "solve" this problem by prequalifying the raw parts they buy, putting them through their own tests to determine which of the parts happen to exceed their specifications and can therefore be "safely" used in the circuit that requires them. This strategy helps somewhat, but it still seems to me like absolute madness.

But, now, to return to the question, what we have here is almost the reverse situation. We have some parts which are known, empirically, to not meet their original specifications at all. We might as well retroactively apply a new set of specifications to a Stab-Lok 20A breaker:

Voltage: 50 VAC
Trip current: 200 A
Interrupting rating: 21 A

And since these effective specifications do not meet the requirements of any electrical installation anywhere, the strong recommendation is to not use the damn things.

But you're proposing an empirical, "postqualification" acceptance test. You're proposing to test a single Stab-Lok breaker, to see if you get lucky, to see if it magically Just Happens to exceed its effective specifications and interrupt an actual short. But even if it does, so what? How many times are you going to repeat the test? What guarantee do you have that the breaker is going to behave the same way tomorrow? What guarantee do you have that, under the slightly different conditions of an actual fault, the breaker is going to trip properly? Do you really want to take that chance? Are you really going to place more faith in the result of your single little small-scale test, over the accumulated experience and wisdom of, basically, everybody? And when actual human lives could be on the line?

Answer 4

Testing a safety equipment is WAY more complex than simply trying a certain failure mode and seeing if the outcome is less than catastrophic.

This method has at least these problems:

1. The failure may get way too expensive in terms of health or lives lost, as well as property damage. In some cases you may burn an appliance few homes away, as well as something belonging to your utility company. Up to and including a prolonged neighbourhood-wide blackout.

2. I am sure there are legal obstacles as well. At least where I live, it is forbidden to connect to the utility grid an appliance that is known to malfunction.

1+2 can get you in the court and the expensive lawyers will not be on your side.

3. The test is profoundly pointless. The test may show that the safety device in question works more or less as intended in your particular test case, once. It may happily fail in another, pretty much legitimate occasion. E.g. the breaker may trip when cold, but may fail when first preheated for an hour by 90% of its rated current. Or when the humidity is low. Or when the moon is in a specific phase and the breaker tripped more than 2 times the last month.

Answer 5

NO.

Short circuiting neutral to ground will not trip a regular breaker. It will probablly trip a GFCI/RCD but it's not really a very meaningful test as the current flow is completely dependent on what loads are present at the time. If you want to test GFCIs/RCDs get the right tool for the job that can prsent a known test current and time to see of the GFCI/RCD trips in the appropriate time. Or just press the test button (which is not an ideal test, but much better than shorting neutral to earth).

Short circuiting live to neutral will result in dangerously high currents, if the breakers fail to do the job of breaking said currents you may have a very dangerous situation on your hands.