Wire size is too small for sub panel?! What should I do?

[gamp945]

I've finally roughed in my small (12x14) workshop and am ready to hook up the sub panel. Currently I have 4 circuits.

As I've posted previously, I ran a 10/2 UF-B wire several years ago before I knew I would ultimately build a workshop. This will provide 30A at 110V and is plenty of power for me as I mostly work with cordless tools (the shop is too small for large machines anyway). I mostly just need a space to work with lights since I don't have a garage. I have no plans to run larger wire as this would be prohibitively expensive (at least $1,000) and unnecessary for my needs.

A while back I purchased a nice copper bus Siemens 12-space load center. This is much larger than I need, but all the reading that I did suggested to go with a larger panel so that adding more circuits in the future would be easy.

Today I read the info on the inside of the panel's door which lists compatible breakers, wire sizes, and torques (see attached photos). I was surprised to see that the smallest compatible main breaker is an MBK100A which requires at least #4 wire, and the installed lugs (listed as terminals A and B) also require at least #4 wire.

Am I correct that there is no way to use this panel with my #10 subfeed wire? If so, I guess I am learning the hard way that there is a major difference between "load centers" and "subpanels" aside from the number of breakers they accept. I have to wonder if people often violate the minimum wire size listed on the panel's lugs or main breaker...the lugs or breaker would screw down on the smaller wire, right?

What are my options? Here is what I can come up with:
1. Find a new panel that accepts at least 4 circuits (preferably full size) and lists #10 wire for the main lugs
***Does anyone know of such a subpanel?***
2. Spend $1,000+ on running #4 wire to the workshop

Does anyone have any other suggestions?

Thanks for reading!

 

[Terry D]

Is this a main breaker or main lug panel. As long as the single pole breaker in your house feeding the sub is not larger than 30 amp you are ok. You will have to jump the buss or main breaker so all the spaces or energized. If this is a detached building, and you are planning on having more than 6 circuits, then you need a main. If it is a main lug panel, then just install a 2-pole 30 and back feed it. you will need a hold down kit. You will have to jump from one pole on the breaker to the other. Problem is the lugs are only rated for one wire. You will just have to pigtail from each and tie them together with your hot feeding it.

Remember to keep your neutrals and grounds isolated and if this is a detached building, install 2 ground rods

Siemens ECMBR2 Hold Down Kit for Back Fed Main Breakers for use on Ultimate, ES, PL, and Murray Rock Solid Load Centers - Circuit Breakers - Amazon.com

Siemens ECMBR2 Hold Down Kit for Back Fed Main Breakers for use on Ultimate, ES, PL, and Murray Rock Solid Load Centers - Circuit Breakers - Amazon.com

www.amazon.com

Is this the panel that you have

Siemens PL Series 125 Amp 12-Space 24-Circuit Main Lug Indoor Load Center P1224L1125CU - The Home Depot

Siemens introduces PL Series Load Centers - a new high quality and feature-rich line of load center products to meet applications for virtually every need. The PL Series load center provides maximum flexibility

www.homedepot.com

 

[wyliesdiesels]

you could splice #4 onto the #10.

as said above you will need a main if more than 6 breaker handles and to energize all breaker spaces you will need to jumper the incoming hot to both sides of the panel.

Perhaps you could splice 2x short pieces of #4 onto the black #10 then connect them to the main breaker or lugs

 

[Terry D]

you could splice #4 onto the #10.

as said above you will need a main if more than 6 breaker handles and to energize all breaker spaces you will need to jumper the incoming hot to both sides of the panel.

Perhaps you could splice 2x short pieces of #4 onto the black #10 then connect them to the main breaker or lugs

Yeah I was going to add to my post, If he is not putting in a main, he could replace the main lugs with ones that accept smaller wire and just use one of the smaller lugs on the neutral buss. If he back fed a 30 amp 2-pole then # 10 would not be to small.

https://www.lowes.com/pd/Blackburn-2-Count-Copper-Lugs/4580085

 

[gamp945]

Terry, you are a life saver!

My panel is a main lug panel (fixed link). And the breaker for the subfeed in the home's main panel is a 30A GFCI breaker.

I did not know that you could "back feed" a panel with a regular breaker. I did a google search and Schneider Electric has a good explanation for the non-pro like myself.

So here is what I think I need to do:
1. Install a 2-pole 30 breaker in positions #1 & #3
2. Install a hold down kit (photo attached shows that Siemens ECMBR2 is correct for my panel)
3. Splice the incoming subfeed #10 wire's hot conductor into two (I have the correct size Wago wire connectors that can be used to do this)
4. Run the two spliced hot conductors to each side of the 2-pole 30A back-fed breaker
5. Install all the other circuit breakers as normal

Have I got all that correct? Thanks again!

 

[Terry D]

Terry, you are a life saver!

My panel is a main lug panel (fixed link). And the breaker for the subfeed in the home's main panel is a 30A GFCI breaker.

I did not know that you could "back feed" a panel with a regular breaker. I did a google search and Schneider Electric has a good explanation for the non-pro like myself.

So here is what I think I need to do:
1. Install a 2-pole 30 breaker in positions #1 & #3
2. Install a hold down kit (photo attached shows that Siemens ECMBR2 is correct for my panel)
3. Splice the incoming subfeed #10 wire's hot conductor into two (I have the correct size Wago wire connectors that can be used to do this)
4. Run the two spliced hot conductors to each side of the 2-pole 30A back-fed breaker
5. Install all the other circuit breakers as normal

Have I got all that correct? Thanks again!

Yep, also make sure you use one of the smaller lugs on your neutral buss since the large one is not rated for # 10

 

[wyliesdiesels]

why is the feeding breaker a GFCI?

 

[gamp945]

Thanks for that additional tip, Terry - I see that the neutral bus does have smaller lugs available for #10-#14.

One more question: when backfeeding a subpanel, do the main lugs remain installed and just end up unused?

 

[Terry D]

I agree with wylies

Thanks for that additional tip, Terry - I see that the neutral bus does have smaller lugs available for #10-#14.

One more question: when backfeeding a subpanel, do the main lugs remain installed and just end up unused?

Yep, just leave them unused.

 

[Ole Slewfoot]

Coil some shim stock around the wire to increase the diameter, wire as normal.
I'm not sure about the 2 conductor wire in you application though, feels like bad juju.

 

[gamp945]

why is the feeding breaker a GFCI?

I thought I remembered reading that the subpanel breaker needed to be GFCI protected. Is this not true? I already have the breaker - should I not use it and instead get a regular (non-GFCI) 30A breaker?

 

[Terry D]

Coil some shim stock around the wire to increase the diameter, wire as normal.
I'm not sure about the 2 conductor wire in you application though, feels like bad juju.

You cant do that

 

[PCustoms]

Coil some shim stock around the wire to increase the diameter, wire as normal.
I'm not sure about the 2 conductor wire in you application though, feels like bad juju.

A 120v feed (2 conductor) is bad juju, but your hack of adding shims to the wire is fine?

WTF.

Op don't wrap with shims, or fold up the wire until it fits. Splice to a short section of larger wire. Less of a fire hazard.

 

[Terry D]

I thought I remembered reading that the subpanel breaker needed to be GFCI protected. Is this not true? I already have the breaker - should I not use it and instead get a regular (non-GFCI) 30A breaker?

If this is a detached building, I personally don't like GFCI protecting underground wire. I would just use GFCI receptacle(s) in the building

 

[gamp945]

If this is a detached building, I personally don't like GFCI protecting underground wire. I would just use GFCI receptacle(s) in the building

It is a detached building. Would you mind explaining why you prefer GFCI receptacles to a GFCI breaker in this application?

Is GFCI protection required at all?

 

[Terry D]

The subpanel itself does not need to be GFCI protected

 

[PCustoms]

Is GFCI protection required at all?

How deep is your wire burried?

 

[Terry D]

It is a detached building. Would you mind explaining why you prefer GFCI receptacles to a GFCI breaker in this application?

Is GFCI protection required at all?

Yes, GFCI protection is required on you receptacles. If your lights plug into receptacles, then they are required also. If they are hardwired, then they are not. The reason I am not a fan of protecting underground wiring is that water may eventually get into the wire and cause nuisance tripping. This is just my opinion.

 

[wyliesdiesels]

Coil some shim stock around the wire to increase the diameter, wire as normal.
I'm not sure about the 2 conductor wire in you application though, feels like bad juju.

horrible idea. dont do that...

Ironic that you think theres something wrong with a 2 conductor w/ grnd feeder...

I thought I remembered reading that the subpanel breaker needed to be GFCI protected. Is this not true? I already have the breaker - should I not use it and instead get a regular (non-GFCI) 30A breaker?

negative. feeding breaker or main disconnect does NOT need to be GFCI protected. And i wouldnt do so. If it trips then youre in the dark. Better to use point of use GFCIs (ie GFCI receptacles) or GFCI branch breakers on the circuits that need it.

 

[gamp945]

Thanks Terry and Wylie for explaining the GFCI issue. I'll install a GFCI outlet at the beginning of each receptacle circuit. The lights are going to be hardwired.

 

[Ole Slewfoot]

A 120v feed (2 conductor) is bad juju, but your hack of adding shims to the wire is fine?

WTF.

Op don't wrap with shims, or fold up the wire until it fits. Splice to a short section of larger wire. Less of a fire hazard.

oh thats got 3 wires, no problem.
Not so much shim till it's tight, just a couple wraps to keep the lug from tearing up the wire. the rental places send us gennies with the camlock pigtails set up like that most of the time and its never been a problem.

 

[alfredeneuman]

the rental places send us gennies with the camlock pigtails set up like that most of the time and its never been a problem.

Rental places are supposed to check their equipment every time they're returned. They're not above some really Mickey Mouse repairs to send them out again.
You were suggesting he wrap a #10 with enough shims to increase the size to #4 (Requiring more than a couple of shims).

 

[Ole Slewfoot]

Yes they check their stuff when it's returned, then they set it up with the stuff we ordered, and that is how they do it.
We pull 200+ KW through it, and it's fine.

Do you even know what shim stock is?

 

[Stuff]

That hold down bracket supposedly only works for breakers 60 amp and above. Size OK as breaker is for disconnect only.

 

[Terry D]

That hold down bracket supposedly only works for breakers 60 amp and above. Size OK as breaker is for disconnect only.

I missed that. Good catch. OP, just use a 2 pole 60, #10 on that will be fine. The single pole 30 in your house feeding your sub will protect the # 10 from be overloaded

 

[alfredeneuman]

Yes they check their stuff when it's returned, then they set it up with the stuff we ordered, and that is how they do it.
We pull 200+ KW through it, and it's fine.

Do you even know what shim stock is?

Do you also suggest the OP check it after every use?
Turning a #10 into a #4 would more would take far more than "just a couple wraps" of shim stock.
What about torque values?
How about some Code violations?
He's asking how to do it right, and your way of doing it is just maximum hacking

 

[Terry D]

Yes they check their stuff when it's returned, then they set it up with the stuff we ordered, and that is how they do it.
We pull 200+ KW through it, and it's fine.

Do you even know what shim stock is?

We know what shim stock is. And this is not the purpose that it is meant for. If he was going to use the main lugs, the easiest thing to do would be to change them to a size that will fit the wire. If your rental equipment burns up. You just take it back and get a replacement. So what happens if the OPs panel burns up.

 

[Ole Slewfoot]

You dont get it, this is whats suplied by the rental company.
How is he going to burn up his panel with a 10 ga supply?

 

[Terry D]

You dont get it, this is whats suplied by the rental company.
How is he going to burn up his panel with a 10 ga supply?

The problem is that we do get it. The size of the wire has nothing to do with it. The little ones burn just like the big ones. I have seen faulty connections on a receptacle which caused it burn and melt. I have seen panels burn and take the house with it. Don't think it cant happen.

 

[gamp945]

I missed that. Good catch. OP, just use a 2 pole 60, #10 on that will be fine. The single pole 30 in your house feeding your sub will protect the # 10 from be overloaded

I think the Siemens Q260 breaker has a minimum wire size of #6 as shown on the photo below, so I think backfeeding a 30A breaker is still the way to go.

As it happens, I already have a 2-pole 30 breaker and the ECMBR2 hold down clamp because I had previously purchased them for an interlock kit to hook up a generator to my home's main panel (which I have not yet done). I can confirm that the hold down clamp (the red piece) does indeed hook into the breaker and screw down onto the panel. However, the black terminal screw cover does not attach correctly to the 30A breaker.

So the hold-down kit does indeed "hold down" but does not protect the terminal screws from someone with a screwdriver. The kit also comes with a "MAIN" sticker to apply to the top of the breaker to warn against using a screwdriver on the terminal screws. Do you think this is this good enough?

I believe main lugs have not been required (or even had the option) of plastic protection covers until quite recently, so maybe it is OK to install the back-fed breaker with the same logic?

 

[Terry D]

I think the Siemens Q260 breaker has a minimum wire size of #6 as shown on the photo below, so I think backfeeding a 30A breaker is still the way to go.

As it happens, I already have a 2-pole 30 breaker and the ECMBR2 hold down clamp because I had previously purchased them for an interlock kit to hook up a generator to my home's main panel (which I have not yet done). I can confirm that the hold down clamp (the red piece) does indeed hook into the breaker and screw down onto the panel. However, the black terminal screw cover does not attach correctly to the 30A breaker.

So the hold-down kit does indeed "hold down" but does not protect the terminal screws from someone with a screwdriver. The kit also comes with a "MAIN" sticker to apply to the top of the breaker to warn against using a screwdriver on the terminal screws. Do you think this is this good enough?

I believe main lugs have not been required (or even had the option) of plastic protection covers until quite recently, so maybe it is OK to install the back-fed breaker with the same logic?

I would say yes. I think the requirement has been out for a couple of code cycles. Not to much else you can do. The main thing is that the hold down will prevent the breaker from coming off the buss. I know it is a code violation, but there are alot of panels installed out there with the lugs exposed. Just if you ever dont feel safe working in there, just turn off the breaker in the house feeding it.

 

[dscheidt]

You dont get it, this is whats suplied by the rental company.
How is he going to burn up his panel with a 10 ga supply?

"Supplied by the rental company" means "done whatever way is cheapest" in my experience, and has nothing to do with safety.

 

[wyliesdiesels]

You dont get it, this is whats suplied by the rental company.
How is he going to burn up his panel with a 10 ga supply?

Because a rental company renting portable tools is the same thing as inside wiring in a building. smh

Good luck getting your jury-rigged install to pass a building inspection

I've seen #14 and #12 wire melted on an outlet (which also melted) because the Shitsco (zinsco) breaker failed to trip on overcurrent (numerous space heaters plugged into same circuit). This is because the connection overheated.

the smaller size of wire will NOT prevent heat build up and using shim-stock on a breaker lug that is NOT NRTL listed for use with shim-stock reeks of hack work. why not just splice the appropriate gauge wire onto the smaller gauge wire and then terminate to spec on the breaker? ya know, like the code-permissive method?

 

[Ole Slewfoot]

I never said he should not, and in fact he easily could at any time after noting high temp rise or making a trip to the store.

 

[gamp945]

Thanks again, Terry. I will definitely turn off the breaker inside the home's panel if I want to work on the workshop panel.

Last night I called Siemens tech support. Surprisingly, open 24 hours. I got an American rep that was much more helpful than your typical call center rep. He could not answer my technical question but took my info and said an engineer would call me in the morning. This morning the engineer called me first thing at 8AM. He explained that the hold down kit is UL listed for a 30-amp double breaker even though there is no way to attach the terminal protector and consequently is code-compliant. He even stated that if my inspector had a problem with the exposed screw terminals that the inspector could call him and he would explain the same.

Very impressed with Siemens tech support - especially since I am just a DIY guy and not a pro!

 

[Terry D]

Thanks again, Terry. I will definitely turn off the breaker inside the home's panel if I want to work on the workshop panel.

Last night I called Siemens tech support. Surprisingly, open 24 hours. I got an American rep that was much more helpful than your typical call center rep. He could not answer my technical question but took my info and said an engineer would call me in the morning. This morning the engineer called me first thing at 8AM. He explained that the hold down kit is UL listed for a 30-amp double breaker even though there is no way to attach the terminal protector and consequently is code-compliant. He even stated that if my inspector had a problem with the exposed screw terminals that the inspector could call him and he would explain the same.

Very impressed with Siemens tech support - especially since I am just a DIY guy and not a pro!

Awesome, let us know how it all turns out!

 

[Stuff]

So the 60 amp minimum for the hold down kit isn't from Siemens but I see it on the advertisers' sites. I sometimes forget that I shouldn't trust what's on their sites.

 

[gamp945]

I did see the on the Amazon listing that it states "60 Amp And Above" but who knows who wrote that.

There is no reference to breaker size on the Siemens website or instruction sheet:

https://support.industry.siemens.com/cs/attachments/109774385/SIE_IS_ECMBR2.pdf

I do think that the instruction sheet should be updated to mention the issue with breakers smaller than 60A.

 

[Stuff]

I did see the on the Amazon listing that it states "60 Amp And Above" but who knows who wrote that.

There is no reference to breaker size on the Siemens website or instruction sheet:

https://support.industry.siemens.com/cs/attachments/109774385/SIE_IS_ECMBR2.pdf

I do think that the instruction sheet should be updated to mention the issue with breakers smaller than 60A.

Yes, the document needs updated. Doesn't mention the line terminal barrier at all.

 

[gamp945]

The printed document is actually newer than the one available on the website and does mention the terminal barrier. Still no mention of the issue with breakers smaller than 60A though.