workshop power problem

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  #1  
Old 02-08-13, 01:04 PM
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Post workshop power problem

Hello everyone! I am new here. My question is about our woodworking shop.

We installed a subpanel in the shop with 2 15amp breakers and the corresponding breaker in the main panel is a double pole 20amp breaker. the kind of breaker that is 2 breakers that have linked switches and a 20 listed on each side. We ran it with #10 wire with ground. (i know just a little about wiring so i might not be using the right lingo but will do my best to describe)

The problem I am having is that the main panel breaker keeps tripping but the breakers in the shop subpanel are not.

I can have the two breakers in the subpanel switched to the off position and then later find that the main panel breaker has tripped. (and this is before I even try to turn the breakers in the subpanel back on. )

Or while the power seems be running fine in the shop all the sudden the main panel breaker will trip but the subpanel breakers will remain on. I then find that the main panel breaker wont let me reset it. keeps flipping over immediately.

I have found that if I unplug everything from the outlets that run off of the subpanel breakers and leave it alone of a short time the breaker in the main panel will then let me reset it. I then plug everything back in and we have power! This is getting old really quick and we are super busy with orders and can't do it all by hand and in the dark!

for reference there are 2 fluorescent lights on a motion sensing switch, a space heater, a small dust collector, small sander, joiner and table saw plugged in here but none of it runs all the time and most not at the same time.

problem isn't that we try to turn the wrong combination of machines on and trip the breaker this tripping is happening even in the overnight when the shop is completely shut down. thanks for any help!!
 

Last edited by twhite; 02-08-13 at 03:26 PM.
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  #2  
Old 02-08-13, 01:25 PM
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My gut says 20 amps is too small for a subpanel and your list of loads say even a 30 amp breaker might be too small. That heater alone is taking one fourth of your available power. What size wire did you run? Was it at least #10?

his tripping is happening even in the overnight when the shop is completely shut down.
Give us the details on how you wired this including the type of wire or cable you used. Of course with those loads on that small of a breaker the breaker may be damaged but lets be sure of the wiring first.

Please in the future use paragraphs. I almost gave up reading your whole post and may have missed some things because it was just too hard to read.
 
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Old 02-08-13, 03:09 PM
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thanks for the note on paragraphs. Ive never used a forum before so it's good to get some info on what works thanks!

As for the wiring. Yes it is #10 with ground. it has an orange casing if that helps. and the 20amp breaker is the kind where two switches are hooked together as one and the 20 is listed on both switches. does that make it 40? sorry i know very little about this but I'm trying to help my husband!

Also, wondering why the breaker in the main panel is tripping and not the subpanel breakers?

And this happens when everything is turned off, including the subpanel breakers and then later in the overnight that breaker in the main panel is tripping. I guess the stuff plugged in is pulling a load even when the breakers are off in the subpanel?

As a side note, we have been using this set up for quite a while maybe 6 months and just started having this problem recently. We tried another breaker (same kind 20 and 20 with shared pole) in the main panel box with the same results.
 
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Old 02-08-13, 04:15 PM
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If this is a detached structure you should not be using orange cable. Orange cable indicates it is NM-b (AKA Romex. Romex is not approved for use outside period. Even if you put it in conduit it still shouldn't be used. Conduit will fill with water over time. As to why the breaker is tripping now could be a combination of things. First the constant overheating and tripping of the breaker may have damaged it.Second water may have damaged the cable you used and it is shorting out.

For your load you probably need a minimum of #8 UF-b cable with three conductors and a ground if direct buried 24" or conduit with three #8 THWN individual wires and one #10 THWN buried 18". These need to be connected to a 40 amp breaker.

There are several other things that must be done that I suspect you didn't do based on how incorrectly the first install was done but we can discuss those in future posts.

If the structure is attached to your house post back for slightly revised comments.
 
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Old 02-08-13, 04:42 PM
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nope structure is not attached. and yes water could be a factor as part of the wiring was already there from an old garden shed. I know the original wiring was done with old metal conduit and could definitely have rusted/corroded by now.

ok so I need to run a new cable like you mentioned and connect it to a 40amp breaker back in the main box. is that breaker I was talking about before a 40 amp? with the 20 listed on each side and the shared pole/switch?

what else do I need to make sure to do?

Thanks!
 
  #6  
Old 02-08-13, 05:36 PM
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is that breaker I was talking about before a 40 amp? with the 20 listed on each side and the shared pole/switch?
No, the breaker you are using is a 20 amp 2 pole breaker and ray has suggested you use a 40 amp 2 pole breaker. If this shop is being used commercially I think I'd suggest reviewing the possible loads you could have in the future and putting in even more than 40 amps and not just enough to get you by today. You have said you used orange #10 romex (NM-B cable), but you didn't say how many wires were in it. Do you know if it was 10-2 w/Grd or 10-3 w/Grd? Was this new orange cable pulled into the old metal conduit? What are the markings on the outside of the cable? Is the orange cable rather flat or is it more round?
 
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Old 02-08-13, 07:07 PM
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I can't thank you all enough for the help you are giving me. and the patience!!! this is great

The shop is not being used commercially. It's used by just one person and we are at maximum capacity for tools and such. It's a really small shop like 250sqft. I don't see a load increase in the future.

the #10 romex is 10/3 w/ grd.

and I need to clarify the cable situation after I did a bit more investigating. There is 12/3 UF-B with ground running from the breaker in the main box down and then the line goes underground. It pops up again just outside the shop (about 15 feet from where it goes down from the main panel and underground). The cable here however doesn't look the same as the 12/3 UF-B cord running from the main panel. It has a white casing and is more round and still has the 3 wires and the ground. (all of this is original to the house to this point). the owners had built the house themselves and I don't think much of this was done to code. but that's what we are working with.

Then the orange 10/3 with ground that I mentioned before runs under the shop, right under the floor boards and into the sub panel that has the 2 15amp breakers. It does not go through the old conduit. just found out from my husband that the old wire got cut accidentally back at that connection right outside the shop and the new 10/3 was used from there to the sub panel.

SOOOOO 12/3 w/ground UF-B from main panel breaker 20amp 2 pole down then somewhere it changes to that white cased wire i mentioned with that has the 3 leads and 1 ground then it's connected to the orange 10/3 that starts right outside the shop runs under the floorboards and up to the subpanel (with no conduit.) subpanel is located inside the shop.
 
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Old 02-08-13, 07:55 PM
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There is 12/3 UF-B with ground running from the breaker in the main box down and then the line goes underground. It pops up again just outside the shop (about 15 feet from where it goes down from the main panel and underground).
That cable is correct for direct burial and a 20 amp breaker.

The cable here [comes up at shed] however doesn't look the same as the 12/3 UF-B cord running from the main panel. It has a white casing and is more round and still has the 3 wires and the ground. (all of this is original to the house to this point).
That would be NM-b and can not be used outside. It probably pre-exists using colored sheaths for NM-b so is probably very old.

Bottom line what you have is not reusable for a variety of reasons including parts of it are wrong type of cable, you may have an incorrect underground splice, and its too small for your load. It should be cut off at each end and buried or you can remove it, your choice.

If you use 1" PVC conduit you will only need to bury it 18" deep and if you ever do need more current you can pull larger wires. For a 40 amp service you would pull two #8 black THWN wires, one #8 white and one #10 green.

I doubt your current subpanel is correct given everything else. At the subpanel you should have an isolated neutral bar and a bonded ground bar. There should also be an eight foot ground rod driven flush with the ground connected to the ground bar with a #6 cable.

If there are places for more then six breakers in the panel you need a disconnect. Even if you don't install six breakers the number of places is the determining factor. Often a main breaker panel is used and the main breaker serves as a disconnect.

Please note you might get by with a 30a service but the amount saved would not be much. Things like electric heat really eat up the current. In fact when you redo the subpanel you need to install a dedicated 120 volt 20 amp circuit in the subpanel for the heater.
 
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