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Old 06-09-2012, 09:35 PM   #1
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Breaker Issue - 60AMP Breaker 'breaking' when it shouldn't - HELP!


Hey all - I tend a summer home that has a main electrical panel, and a 'guest cabin' that has a sub-panel.

The main panel has a 60Amp fuse that powers the sub-panel in the guest cabin.

The panel in the guest cabin has a 100AMP main switch.

First question: Is it odd to have a 100Amp panel in the guest cabin with only a 60Amp fuse in the main panel?


The reason that I am posting here is because the dryer (there is a washer/dryer in the guest cabin - both electrically powered) is randomly causing the 60Amp fuse in the main panel to snap - so that I have to go under the cottage and turn it all the way off, and then back on again in order to get power back to the sub panel in the guest cabin.

I pulled out the dryer today and checked the vent - all clear!

Here is what is confusing me - the sub-panel in the guest cabin has a 30amp fuse for the dryer - which is NOT snapping.

Also - the only other electric devices being used at the same time are the fridge and some 15watt energy efrficient lights.

The fridge/lights are on a 15amp fuse - the dryer is on a 30 amp. Even if these were MAXING out that is only 45 amps. Why the heck is the 60Amp fuse snapping in the main panel?

Only the dryer seems to put the strain necessary to make this happen.

Any thoughts?

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Old 06-09-2012, 10:54 PM   #2
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Breaker Issue - 60AMP Breaker 'breaking' when it shouldn't - HELP!


Not odd to have a 100 amp panel fed by a 60 amp circuit. 100 amp panel are often cheaper than 60 panels.
I assume you have breakers and not fuses. The problem could be that the 60 amp breaker is defective. The way to be sure is to put a ammeter on the feed to the cabin and see what the draw is.

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Old 06-10-2012, 04:54 PM   #3
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Breaker Issue - 60AMP Breaker 'breaking' when it shouldn't - HELP!


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randomly causing the 60Amp fuse in the main panel to snap

has a 30amp fuse for the dryer - which is NOT snapping.
-A transient short circuit upstream of the 30A and downstream of the 60A.

-The trip curve of the 60A breaker is fewer amps than the 30A breaker at some levels of current >60A. To confirm this you'd have to pull up the trip curves of both devices.

The dryer current draw may somehow contribute to this intermittent problem or it is a coincidence.
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Old 06-10-2012, 05:06 PM   #4
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Breaker Issue - 60AMP Breaker 'breaking' when it shouldn't - HELP!


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Originally Posted by joed View Post
Not odd to have a 100 amp panel fed by a 60 amp circuit. 100 amp panel are often cheaper than 60 panels.
I assume you have breakers and not fuses. The problem could be that the 60 amp breaker is defective. The way to be sure is to put a ammeter on the feed to the cabin and see what the draw is.
I agree Joe or it could be a water heater starting up with the dryer.

Any other loads like a well pump?
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Old 06-10-2012, 05:10 PM   #5
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Breaker Issue - 60AMP Breaker 'breaking' when it shouldn't - HELP!


There is a water heater in the cabin. I thought this as well. The 20amp for the water heater plus the 30amp for the dryer could cause the issue.

However, I turned off the water heater breaker, and the issue still occured.

PS - I have no idea what a trip curve is or how to measure it.
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Old 06-10-2012, 07:28 PM   #6
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Breaker Issue - 60AMP Breaker 'breaking' when it shouldn't - HELP!


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PS - I have no idea what a trip curve is or how to measure it.
Reading trip curves is a bit confusing and that probably isn't the problem anyway.

But you can search on

"trip curve" Square d

In any case you need to find some way to reliably make the problem show up.
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Old 06-10-2012, 08:40 PM   #7
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Breaker Issue - 60AMP Breaker 'breaking' when it shouldn't - HELP!


Cliff note version of trip curve....

Breakers are designed for different types of loads.....the trip cure determins how much current at any given moment a breaker will tollerate before it trips....the current trip point is actually on a curve....

For example...resistive loads (electric heaters and light bulbs) should have a fairly short trip curve....for the first few ms they can tollerate say 200% of the current....but the current limit will go down quickly...so if the load continues above the load limit if the breaker for too long...it trips.

Whereas, a motor needs a longer trip curve to allow for startup. It may have the same initial startup current...but the curve is longer and will tollerate higher currents before it trips...this allows the motor time to start up.

Curves are typically designated as A, B, C.

If you don't find any good info on Square D, try the ABB site....Square D's web site is not the easiest to navigate.

I just dug up this reference.....I think it explains it pretty good.

http://www04.abb.com/global/seitp/se...r+Volume+1.pdf
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Old 06-10-2012, 08:57 PM   #8
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Breaker Issue - 60AMP Breaker 'breaking' when it shouldn't - HELP!


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Originally Posted by LordX View Post
There is a water heater in the cabin. I thought this as well. The 20amp for the water heater plus the 30amp for the dryer could cause the issue.

However, I turned off the water heater breaker, and the issue still occured.

PS - I have no idea what a trip curve is or how to measure it.
Sounds like you're trying all the right things.

What's left:

weak 60A breaker?
un-responsive 30A breaker?
shorted feed to cabin?
some load you haven't found?

Close to calling an electrician?

Don't feel bad, you've done as much w/o instruments as anyone could expect.
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Old 06-10-2012, 09:34 PM   #9
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Breaker Issue - 60AMP Breaker 'breaking' when it shouldn't - HELP!


Turn off power and pull the 60 amp breaker protecting the feeder to the guest cabin. Inspect it and the panel bus stabs for any arcing marks. Often you cannot see this without the breaker removed. I'm suspecting that heat build up on the connections to the bus stab and breaker are causing the thermal trip to activate and open the breaker. There are some panels and breakers that are more prone to this problem. What is your panel manufacturer? Is the 60 amp breaker a listed breaker ie correct breaker for the panel?
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Old 06-11-2012, 08:51 PM   #10
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Breaker Issue - 60AMP Breaker 'breaking' when it shouldn't - HELP!


Replaced the 60Amp circuit and all seems ok!

There was a dead mouse behind the old breaker - no idea if this was the cause or not - but who knows.

PS - 12 years ago this 60 amp breaker was $18.99..... today from the SAME store it was $49.99!!!! ouch!
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Old 06-13-2012, 05:00 PM   #11
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Breaker Issue - 60AMP Breaker 'breaking' when it shouldn't - HELP!


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is randomly causing the 60Amp fuse in the main panel to snap
If it snaps every d days on average you need to have 3 x d consecutive days without a trip to be pretty sure you have fixed the problem.

BTW, and speaking of trip curves, it's easier to check large, costly breakers than small cheap ones.
You need a clamp-on ammeter, a car battery and a few feet of #16 copper or iron wire, immersed in motor oil (for cooling).
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Old 06-13-2012, 05:40 PM   #12
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Breaker Issue - 60AMP Breaker 'breaking' when it shouldn't - HELP!


It tripped every 2-4 minutes when running the dryer along with anything else (e.g. the fridge).

So when we were able to complete 2-3 LOADS of laundry - that is many times 2-4 mins. So hopefully the issue is truly resolved!
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Old 06-13-2012, 05:54 PM   #13
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Breaker Issue - 60AMP Breaker 'breaking' when it shouldn't - HELP!


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It tripped every 2-4 minutes when running the dryer along with anything else (e.g. the fridge).

So when we were able to complete 2-3 LOADS of laundry - that is many times 2-4 mins. So hopefully the issue is truly resolved!
Sounds good to me.
Post-game analysis, I guess your old breaker was tripping at less than 30A.

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