240 on 480v

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mannyb

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Electrician
Can I installed a 240v breaker or fuse on 480v or 277v.
We are havin a discussion on Sunday so forgive us for questions.

They want to install a 120v breaker on a 277v conductor but increase the amperage. I have never done that but I would imagine it would fail adding 277v to a single 120v breaker. I'm not dping this and it may be a discussion for another thread but I Sunday and Im at work.
 
mannyb said:
Can I installed a 240v breaker or fuse on 480v or 277v.
We are havin a discussion on Sunday so forgive us for questions.

They want to install a 120v breaker on a 277v conductor but increase the amperage. I have never done that but I would imagine it would fail adding 277v to a single 120v breaker. I'm not dping this and it may be a discussion for another thread but I Sunday and Im at work.
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Ive seen a lot of things work that should never have.

what exactly are you trying to do?
 
With a lower voltage breaker, it will carry the current just fine but there are two major risks:
1. The insulation might break down causing an arc inside the breaker, and
2. The breaker contacts might not survive opening under load at the higher voltage.

With a fuse, as long as the fuse holder is rated for the higher voltage the first risk is essentially zero, but risk that the fuse opening will not properly interrupt the circuit (clearance time increased if nothing else) is just as high.

As far as code compliance goes, both are an absolute NO.
 
ptonsparky said:
Ive seen a lot of things work that should never have.

what exactly are you trying to do?
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A 60a 600v fuse failed and it's Sunday and we can't get a replacement. One of the guys wants to buy a 120v breaker at 120amp to make it work. He says the 277v isn't the issue it's the amperage. My guess the 120v breaker won't take the 277v.
 
mannyb said:
A 60a 600v fuse failed and it's Sunday and we can't get a replacement. One of the guys wants to buy a 120v breaker at 120amp to make it work. He says the 277v isn't the issue it's the amperage. My guess the 120v breaker won't take the 277v.
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The 277 is an issue plus you want to double the current available...

Find a fuse or shut the system down for the weekend. Your treading dangerous waters.
 
One of the risks of using an under-rated fuse or breaker is that the contacts might not be far enough apart when it opens, enabling an arc to jump the gap and enabling current to continue to flow, even though the breaker contacts have opened or the fuse wire has melted.
 
mannyb said:
A 60a 600v fuse failed and it's Sunday and we can't get a replacement. One of the guys wants to buy a 120v breaker at 120amp to make it work. He says the 277v isn't the issue it's the amperage. My guess the 120v breaker won't take the 277v.
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So this person is proposing to use a 120 amp breaker to protect a 60 amp circuit?

That's not good, you know.

That's aside from using an underrated device. What good are voltage ratings if they can be ignored?
 
drcampbell said:
One of the risks of using an under-rated fuse or breaker is that the contacts might not be far enough apart when it opens, enabling an arc to jump the gap and enabling current to continue to flow, even though the breaker contacts have opened or the fuse wire has melted.
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Thus the difference in physical size of a 12 volt 60 amp fuse and a 600 volt 60 amp fuse.
 
Check the breaker itself as well.... I have used breakers before that were marked for multiple voltages... Schneider has many such that have differing curves at different voltages
 
Adamjamma said:
Check the breaker itself as well.... I have used breakers before that were marked for multiple voltages... Schneider has many such that have differing curves at different voltages
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Are you referring to slash rated breakers?

Never heard of a breaker with adjustable voltages, adjustable trip settings are something else.

You have a link to these breakers?
 
They are not adjustable. But they have different ratings at different voltages. Mostly in Europe catalogues and for use in commercial rather than residential, but, have seen them rated for 400/240/120 before... with various response times at each voltage and maximum response listings.

As said, Schneider has them for various voltage settings. Pretty sure GE has them as well, but been fifteen years since I looked in GE catalogues
 
Adamjamma said:
They are not adjustable. But they have different ratings at different voltages. Mostly in Europe catalogues and for use in commercial rather than residential, but, have seen them rated for 400/240/120 before... with various response times at each voltage and maximum response listings.

As said, Schneider has them for various voltage settings. Pretty sure GE has them as well, but been fifteen years since I looked in GE catalogues
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Any breaker can be used at a lower voltage than its full voltage rating, just not at a higher voltage.
 
mannyb said:
A 60a 600v fuse failed and it's Sunday and we can't get a replacement. One of the guys wants to buy a 120v breaker at 120amp to make it work. He says the 277v isn't the issue it's the amperage. My guess the 120v breaker won't take the 277v.
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Mostly do resi so a little ignorant here, there is a 120 volt 120 amp breaker? It doesn't sound like a 120 amp breaker would be available either on a Sunday.
 
GerryB said:
Mostly do resi so a little ignorant here, there is a 120 volt 120 amp breaker? It doesn't sound like a 120 amp breaker would be available either on a Sunday.
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120 ampere is not even a standard size, and even a 100 ampere single pole breaker is pretty rare, I have only seen one & it's in my stash somewhere.
 
GerryB said:
Mostly do resi so a little ignorant here, there is a 120 volt 120 amp breaker? It doesn't sound like a 120 amp breaker would be available either on a Sunday.
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No, the OP said a 60A fuse (rated at 600V) blew/failed and someone wanted to use a 120A breaker to power the circuit back up.
 
No one mentioned this so I will. The 60A fuse blew for some reason. If you put in a 120A breaker you risk either melted wire or fire or both.
 
No we didnt and werent going to install the low voltage to higher voltage. The guys did make a good argument and I actually wanted to see if it would work but i wasnt going to be the one to do it. I was just wondering with over 100s of years of experience on this forum some tried it at least once or seen it done.

Thanks guys
 
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