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troubleshooting my new electric sub panel tripping breakers with TS

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Forum topic by jamsomito posted 12-06-2018 05:25 PM 4133 views 1 time favorited 100 replies Add to Favorites Watch
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jamsomito

311 posts in 629 days


12-06-2018 05:25 PM

I saved my pennies and hired an electrician to install a 50A subpanel in my garage. It was put in Monday and I’ve taken the last couple nights to put the shop back together. Yesterday I fired up my heater, shop vac, and table saw at the same time just to test it out and everything seemed fine, except the shop vac bogged down a bit while the table saw spun up. I thought I would have ample juice, but everything is coming over a 6ga wire so wrote it off as that.

Today I went in the shop to get some work done and my table saw is now tripping either of the 2 new breakers that were put in. It will fire up and run once in a while, but most of the time it trips. I noticed it is not bogging down the shop vac like it did yesterday, just a little dip right when the saw is fired up, but not an elongated struggle to start. But now I have the tripping problem.

I tried both of my new 20A circuits, and same behavior. I tried my old 15A garage circuit that I’ve been using for years it it did it’s typical chugalug startup but eventually got running and did not trip that breaker, as has been the norm for the last several years.

My saw is an old Powermatic 63 – 1-3/4 HP, 120V.

Any thoughts? Should I have my electrician back or do you think it’s an issue with the saw?


100 replies so far

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GrantA

742 posts in 1610 days


#1 posted 12-06-2018 05:30 PM

You’re running on the ragged edge. That saw really needs it’s own 20a circuit. I’m surprised it has been satisfactory on a 15a but your chugalug comment is troubling. Is the heater still running too? What are specs on that? It’s probably 20+ too, then the shop vac can eat up 15, you’re over capacity

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jamsomito

311 posts in 629 days


#2 posted 12-06-2018 05:36 PM


You re running on the ragged edge. That saw really needs it s own 20a circuit. I m surprised it has been satisfactory on a 15a but your chugalug comment is troubling. Is the heater still running too? What are specs on that? It s probably 20+ too, then the shop vac can eat up 15, you re over capacity

- GrantA

To clarify, here’s a couple scenarios:
new 20A circuit #1: table saw
new 20A circuit #2: shop vac
old 15A circuit: IR heater
SAW TRIPS

old 15A circuit: table saw
Chugs to start, but runs fine.

No matter if I plug the TS into the new circuit #1 or #2 (both 20A), it trips the associated new 20A breaker. I understand if the 50A breaker for the panel trips, but I do’nt get why ONLY the table saw breaker trips. It’s 20A. It’s odd to me that that trips while the 15A garage circuit doesn’t – although maybe the wire is small enough to limit power draw enough that it can’t actually trip. It has been unsatisfactory for the last several years, but it only trips when under heavy load.

My heater was not going through the sub panel, but another 15A circuit on my main panel. It’s a 1000W electric radiant heater, so figure maybe 10A.

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GrantA

742 posts in 1610 days


#3 posted 12-06-2018 05:40 PM

OK that clears it up a bit. It sounds like you might need to get the electrician back out.

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HokieKen

7130 posts in 1341 days


#4 posted 12-06-2018 05:41 PM

Are the new breakers GFCI or AFCI? Maybe a wiring issue somewhere in your saw that wasn’t caught by a standard breaker but is caught now due to the nature of the fault.

I have the same saw and when I got it, it was wired for 115V. When I ran it on a 15 A circuit, I could trip the breaker depending on the load I was putting on it. I re-wired the motor for 230 and ran a new circuit and haven’t had any problem since. Something to consider. You should have the capacity for a 230V, 20A circuit on that panel.

-- Kenny, SW VA, Go Hokies!!!

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jamsomito

311 posts in 629 days


#5 posted 12-06-2018 05:46 PM



Are the new breakers GFCI or AFCI? Maybe a wiring issue somewhere in your saw that wasn t caught by a standard breaker but is caught now due to the nature of the fault.

I have the same saw and when I got it, it was wired for 115V. When I ran it on a 15 A circuit, I could trip the breaker depending on the load I was putting on it. I re-wired the motor for 230 and ran a new circuit and haven t had any problem since. Something to consider. You should have the capacity for a 230V, 20A circuit on that panel.

- HokieKen

Good questions, and I had exactly the same problems on my old 15A circuit. I have plans to try 220V, but I won’t have time for that until probably this next summer. In the meantime I figured a good clean 20A 120V circuit would be a big upgrade from what I had though.

The subpanel feeder is coming off a 50A GFCI breaker on my main panel. This way the whole subpanel is protected and it avoids needed every new circuit for the garage to have a new GFCI breaker – I can just use regular breakers there. It’s possible this is tripping the local regular breakers, but I just don’t know enough about it to say for sure. It seems to me if the GFCI protection was the problem that it would trip the 50A breaker in my main panel, not the 20A standard breaker in the subpanel.

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DBDesigns

183 posts in 200 days


#6 posted 12-06-2018 05:56 PM

Hokie has a point about rewiring the saw to 230v. It will use less power that way and your new sub-panel should handle a new 230 v circuit just fine.

Also, don’t overlook the possibility that you may have bad breakers from the manufacturer. Everything is made overseas these days and their quality standards are not what we are used to. The fact that the saw works fine on the old circuit implies that it is fine, just too much draw.

I would call the electrician and ask some pointed questions before I had him come back.

-- I remember when Grateful wasn't Dead

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HokieKen

7130 posts in 1341 days


#7 posted 12-06-2018 05:59 PM

I agree. I don’t think it’s the GFCI. That breaker should be thrown if so.

What I would do briefly and just for a quick test is to swap the 15A breaker in the main panel and one of the 20A breakers in the subpanel. Then see if both still act the same way. Do not leave it this way because the wire in the 15A circuit is too small for a 20A load. But, if you do that and the 20A breaker acts like it should and doesn’t trip but the 15A does trip, it’ll tell you that there’s something in the wiring from the main to the subpanel. If that is the case, make the electrician fix it.

-- Kenny, SW VA, Go Hokies!!!

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GrantA

742 posts in 1610 days


#8 posted 12-06-2018 06:03 PM

Kenny I remember from his other post that he had a QO panel put in the garage, most houses aren’t. My electrician looked at me like I was nuts when I specced all QO stuff (about 7yrs ago when we built). It’s just now the norm. Homeline, or some other brand are more popular. All that said meaning he may not be able to swap them. You plan to add more circuits anyway though so maybe just pickup a 20a breaker to try but I doubt you got 2 that are bad

Do you have a non-GFCI circuit near enough to try that? Is the old 15a circuit also GFCI? Strange things can happen on those

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HokieKen

7130 posts in 1341 days


#9 posted 12-06-2018 06:14 PM

AFAIK, QO works the same as any other panel/breaker, right? I don’t know much about it other than my son just had a QO subpanel installed in his garage.

I agree fully that GFCI can act funny. And, in fact, substantial current swings can cause it to trip even when the swings are normal operation. But, I don’t see how it would cause his subpanel breaker to throw but not throw the GFCI breaker the sub is ran off of.

Then again, I’ve always said electricity is black magic and only soulless demons can harness its power. So I’m far from an expert in the field ;-)

jamsomito – if Fridge doesn’t chime in on this thread, shoot him a PM. He’s one of those dark wizards and knows his stuff up one side and down the other. He’ll be able to tell ya which finger to lick and where to stick it ;-)

-- Kenny, SW VA, Go Hokies!!!

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GrantA

742 posts in 1610 days


#10 posted 12-06-2018 06:18 PM

I just meant unless he has QO in the house he can’t try that breaker in the new QO panel ;-)
aha! Now I know how to tag someone, Kenny will it notify Fridge that you tagged him?

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HokieKen

7130 posts in 1341 days


#11 posted 12-06-2018 06:21 PM

Duh… Didn’t think about that. ;-)

-- Kenny, SW VA, Go Hokies!!!

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jamsomito

311 posts in 629 days


#12 posted 12-06-2018 06:22 PM

lol, ok thanks. Yes, it is a Square D QO panel. My main panel is a Cutler Hammer, so I was under the impression that the breakers are non-interchangeable. Those are all 20 years old though, so I didn’t foresee the need to swap any.

The 15A circuit in my garage is indeed GFCI, though that has a local GFCI outlet that all other garage outlets stem from (just a regular breaker). The garage door opener is on the same circuit, not GFCI protected.

I thought it could be a bad breaker on my new panel as well, but also agree it might be a stretch that both of mine are bad…

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HokieKen

7130 posts in 1341 days


#13 posted 12-06-2018 06:22 PM


Now I know how to tag someone, Kenny will it notify Fridge that you tagged him?

- GrantA

Nope. I didn’t really “tag” him. I just hyperlinked his home page. No tagging on LJs…

-- Kenny, SW VA, Go Hokies!!!

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GrantA

742 posts in 1610 days


#14 posted 12-06-2018 06:26 PM

that’s a shame, I thought I tagged him in another oak post haha

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DBDesigns

183 posts in 200 days


#15 posted 12-06-2018 06:28 PM

Y’all are underestimating the capacity of the Chinese to produce inferior products. Hell I wouldn’t be surprised if they shipped an entire container full of bad breakers!

-- I remember when Grateful wasn't Dead

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