Powering shunt-trip coil from load side of shunt trip breaker?

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Jon456

Jon456

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Colorado
I need to disconnect all power at a subpanel with an e-stop switch. I will be installing a shunt-trip breaker upstream of the subpanel. I want to provide power to the momentary N/O e-stop switch (which will activate the shunt-trip if the "mushroom" is pressed) from the load side of the shunt trip breaker.

1. The shunt trip breaker is rated at 40A. The terminals for the shunt-trip are rated for max #12AWG. I do not want to take power from a 15A or 20A breaker in the downstream subpanel because, if that breaker is ever tripped or switched off, the e-stop will not function. So I want to pull power for the e-stop/shunt-trip circuit directly off the load side of the shunt-trip breaker. I have read about doing this in several threads about wiring shunt-trip breakers. What I haven't seen addressed is how to protect the e-stop/shunt-trip wiring. If there is a dead short in the e-stop/shunt-trip circuit, I expect the 40A breaker will trip. And it seems I don't really have to worry about overloading the wiring, as the shunt-trip coil is rated to draw only 0.6A at 120VAC. So do I need to install an in-line fuse for this dedicated e-stop/shunt-trip circuit? Or is that unnecessary? If it makes a difference, all the wiring for the e-stop/shunt-trip circuit will be in EMT conduit.

2. For those who have wired shunt-trip breakers in this manner, how do you tap power off the load side of the shunt-trip breaker? I believe double-lugging the #12 shunt-trip circuit wires to the load-side lugs of the breaker is not permitted unless specifically L&L by the breaker's manufacturer. But Polaris connectors (or wire nuts) on the feeder conductors between the shunt-trip breaker and subpanel seems rather clunky.
 
You will need to provide over current protection.

Just power it up from a circuit in the panel that will not be shut off.
 
iwire said:
You will need to provide over current protection.
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That's what I suspected. Just out of curiosity, why is equivalent over-current protection not required inside manufactured equipment? This is a dedicated, current-limited circuit, so why wouldn't be similarly exempt?

iwire said:
Just power it up from a circuit in the panel that will not be shut off.
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The subpanel is in an accessible location and I do not intend to put my trust in a circuit breaker that could be manually turned off. I will add a fuse block inside the shunt-trip breaker enclosure.
 
Have you thought about using fail safe logic. You could use NC contacts on a 120v relay held open by power through a NC e-stop. If the anything every fails it will fail safe.

It is definitely complicates things though, but most e-stop s I've seen are fail safe.


EDIT:

Probably won't work. Depending on breaker shunt trip time....I think it would be a relay race situation and trip the breaker at power up
 
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Saturn_Europa said:
Have you thought about using fail safe logic. You could use NC contacts on a 120v relay held open by power through a NC e-stop. If the anything every fails it will fail safe.

It is definitely complicates things though, but most e-stop s I've seen are fail safe.


EDIT:

Probably won't work. Depending on breaker shunt trip time....I think it would be a relay race situation and trip the breaker at power up
Click to expand...

This would not fix the issue of a reliable source of power to open the shunt.

To me this is the draw back of using shunt breakers in place of normally open contactors.
 
Jon456 said:
That's what I suspected. Just out of curiosity, why is equivalent over-current protection not required inside manufactured equipment? This is a dedicated, current-limited circuit, so why wouldn't be similarly exempt?
Click to expand...

Well the wiring in manufactured equipment stays contained in that enclosure, your shunt trip circuit has field wiring to somewhere right?


The subpanel is in an accessible location and I do not intend to put my trust in a circuit breaker that could be manually turned off.
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This panel has no existing 15 or 20 amp circuits you could power the shunt from?

In other words if the circuit gets turned off it would shut off a needed / used circuit and would be turned back on.



I will add a fuse block inside the shunt-trip breaker enclosure.
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If you want to go that way I suggest using this style of finger safe, fuse holder & disconnect.

http://www.alliedelec.com/bussmann-...PU51WYempyLGNogsJNRIY3jLMbfXmyMDNEaAmqf8P8HAQ

70264459_large.jpg



Many companies make them, some even have trip indicator LEDs

You will need a little bit of DIN rail to mount them.
 
Jon456 said:
I do not want to take power from a 15A or 20A breaker in the downstream subpanel because, if that breaker is ever tripped or switched off, the e-stop will not function.
Click to expand...

Why not just install an E-stop with a lighted button or indicator and a handle lock on the breaker? You are not addressing the potential of a tripped shunt circuit by installing a fuse block, only making it harder to detect when tripped and harder to change the fuse if it does.

5B735_AS01.jpg
 
If this were a motor control circuit table 430.72(B) would allow a 12 awg control conductor to be protected up to 60 amps.

Unfortunately I can't see how one can apply that if there isn't motor controls on the same control circuit.

I don't see what supplementary protection would hurt, even if it were an inline fuseholder at the point where this control circuit gets tapped to the power circuit.
 
iwire said:
One of us has misunderstood the other.:huh:

As far as reliability I have always felt normally open contactors where better / safer than shunt trip breakers.

Shunt trips are cheaper and easier but IMO now and in the past less reliable.

Do you have me confused with Jim D? :?
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Take a look at #13 on the page I linked to. Unless there is another "iwire" running around you said:

"As a side note, I prefer breakers for reliability."
 
gadfly56 said:
Take a look at #13 on the page I linked to. Unless there is another "iwire" running around you said:

"As a side note, I prefer breakers for reliability."
Click to expand...

Hmm, either I was messing with you or I was talking from a 'staying on' standpoint.

If I had a mind to I could dig up many post where I advocate contactors.
 
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