sub panel hookup

[Bruce4310TX]

Starting to plan my 30 x 50 shop with 100 amp service, Question why do you use feeder breakers in the main panel for the sub panel is it to isolate the sub ? whats wrong with hooking up to main panel service lugs and use a sub with a main disconnect..... I am not doing this just always wondered why not. Thanks

 

[timewarp]

To protect the wires from the main panel to the sub panel.

 

[Bruce4310TX]

I agree but if you have a main breaker in the sub its still protected

 

[Gary S]

I agree but if you have a main breaker in the sub its still protected

Not really. I don't believe code allows you to have a 100 amp subpanel on a 100 amp main panel.
So, lets say that you put a 100 amp sub panel on a 200 amp main panel. Now, the main panel has breaker protection for 200 amps, and your sub panel has wiring from the main to the sub rated only at 100 amps. See the problem?
You want a 100 amp breaker in the main panel subfeeding the 100 amp wire and the 100 amp sub panel to protect this wiring.

 

[MrMark]

I agree but if you have a main breaker in the sub its still protected

Right. It's protected in either place. The wire doesn't care if the breaker is in the beginning or the end. The same current is flowing thru the wire at each end.

I don't know the answer to this question, but it is a good question.

 

[travisd]

Right. It's protected in either place. The wire doesn't care if the breaker is in the beginning or the end. The same current is flowing thru the wire at each end.

I don't know the answer to this question, but it is a good question.

Not if there's a short between the Main and Sub though...

 

[walrus]

I agree but if you have a main breaker in the sub its still protected

No, its not. if there is a short between the main and the sub, the sub panel breaker isn't going to trip and if there isn't one in the main, the wire is going to burn or the connections are going to burn.

 

[Jack Davenport]

It's like evryone else has stated "to protect the wire from the panel to the sub panel".
That and what you described would be what is referred to as a feeder tap.
There are very specific rules about how and the length of feeder taps in the National Electrical Code. You garage would not come close to qualifying.

 

[Aceman]

Not really. I don't believe code allows you to have a 100 amp subpanel on a 100 amp main panel. So, lets say that you put a 100 amp sub panel on a 200 amp main panel. Now, the main panel has breaker protection for 200 amps, and your sub panel has wiring from the main to the sub rated only at 100 amps. See the problem?
You want a 100 amp breaker in the main panel subfeeding the 100 amp wire and the 100 amp sub panel to protect this wiring.

That's a myth.

If the sub is the same size as the main panel you can usually just use a feed through lug kit to fit the main panel. There's no sense using a 100 amp feeder breaker to feed the subpanel when the main breaker in the main panel is already 100 amp. Hopefully that made sense...

 

[MrMark]

Not if there's a short between the Main and Sub though...

True, but the main would certainly trip on that. I suppose that a fault condition in the wire run that was not a dead short could occur. I can't think of what it would be . . .

It would have to be a condition that was very strange. Something short of a dead short in a wire between two panels. It would have to be a current more than the 100 amp breaker at the sub and less than the 200 amp at the main to be an issue.

I see why it is done the way it is done, though.

 

[Gary S]

That's a myth.

If the sub is the same size as the main panel you can usually just use a feed through lug kit to fit the main panel. There's no sense using a 100 amp feeder breaker to feed the subpanel when the main breaker in the main panel is already 100 amp. Hopefully that made sense...

It makes excellent sense. I wasn't aware that you were allowed to subfeed a sub panel of equal size. Since it is allowed, then the extra 100 amp breaker in the main to feed the sub would be redundant.
My concern here was that the original poster might not have panels of equal current rating. If the main panel is fused larger than the wire that runs between the main and the sub, the protection would be inadequate.

 

[Norcal]

How is the original poster intend to tie in the subfeed? The whole thing reeks of stuffing the subfeed conductors into the lugs of the main panel w/ the SE conductors, which is wrong in a number of ways, 1) it's "double lugging", 2) The SE conductors ahead of the main have no overcurrent protection at all, 3) tap rules do not apply in what the OP is proposing....

 

[Bruce4310TX]

Norcal, your correct thats what my question asked about tapping into the main lugs,,,,, No i am not planning on doing that just wondering why it cant be done if your sub panel has a main shut off also. My house has 400 amp service its all electric i have plenty of unused capacity. just looked at the box and asked my self why not ??? I dont have the answer.

 

[Norcal]

Norcal, your correct thats what my question asked about tapping into the main lugs,,,,, No i am not planning on doing that just wondering why it cant be done if your sub panel has a main shut off also. My house has 400 amp service its all electric i have plenty of unused capacity. just looked at the box and asked my self why not ??? I dont have the answer.

If you tap ahead of the main & there is a fault in the feeder to your subpanel ahead of a overcurrent device, there is absolutely no protection of the feeder, for that reason IMO it's a bad idea. Power companies have no overcurrent protection on their transformer secondary conductors.

 

[JBurgess]

Is the garage attached or detached?

Is the meter inside or outside?

Is the main panel inside or outside?

Are you in the US?

 

[Bruce4310TX]

Is the garage attached or detached?

Is the meter inside or outside?

Is the main panel inside or outside?

Are you in the US?

Detached, outside, inside, yes. its a standard setup.

The main problem i see if you tapped into the Main lugs for the sub panel and this wire shorted before your sub main breaker that would be a problem, but properly installed and protected what other drawback would there be ? granted that run of wire would always be hot

 

[kool55]

I istalled a sub panel on the other side of my shop last year. The feeder is tapped from a 125 amp CB in the 200 amp main panel. When I work on the sub I turn off the 125 in the main and everything at the sub is safe .At the same time I am not affecting any of the circuits in the main.

 

[Norcal]

I istalled a sub panel on the other side of my shop last year. The feeder is tapped from a 125 amp CB in the 200 amp main panel. When I work on the sub I turn off the 125 in the main and everything at the sub is safe .At the same time I am not affecting any of the circuits in the main.

Is that 125 A permitted by the manufacturer? A lot of panels are limited to 110*A per bus stab, only reading the panel label will tell for sure. A tap & a overcurrent device placed near the service equipment to protect the feeder could work for the OP.

*110A is a "standard" size breaker but would be more likely to be a $pecial order item.

 

[JBurgess]

Detached, outside, inside, yes. its a standard setup.

The main problem i see if you tapped into the Main lugs for the sub panel and this wire shorted before your sub main breaker that would be a problem, but properly installed and protected what other drawback would there be ? granted that run of wire would always be hot

As I understand, any feeder to the detached garage originating inside the house, would be required to have proper overcurrent protection.

However if the feeder originated from a tap in meter socket outside the house and is always outdoors, other than being a poor choice safety wise and dificult to service, would 240.21 (B) (5) Apply?

 

[kool55]

Is that 125 A permitted by the manufacturer? A lot of panels are limited to 110*A per bus stab, only reading the panel label will tell for sure. A tap & a overcurrent device placed near the service equipment to protect the feeder could work for the OP.

*110A is a "standard" size breaker but would be more likely to be a $pecial order item.

The sub panel is a 125 amp main lug. Just thought , are you asking about the main panel? It says 225 max but nothing about a single circuit. My 125 breaker is a 2 pole so that would be 62 amps per bar. No?

 

[oleguy]

no...125amp per side.

 

[Norcal]

The sub panel is a 125 amp main lug. Just thought , are you asking about the main panel? It says 225 max but nothing about a single circuit. My 125 breaker is a 2 pole so that would be 62 amps per bar. No?

Each pole of the circuit breaker is 125 amperes, that is the reason I asked in the earlier post because there is a limitation in many panels of the maximum breaker size allowed per bus stab in a panel, reading the panel label is about the only way to be sure. And yes the main panel is the one am asking about.

 

[sberry]

What brand is this 225 main panel?

 

[Torque1st]

The sub panel is a 125 amp main lug. Just thought , are you asking about the main panel? It says 225 max but nothing about a single circuit. My 125 breaker is a 2 pole so that would be 62 amps per bar. No?

You need a main disconnect at the sub panel.

A 125A breaker is 125A per pole.

 

[oleguy]

What brand is this 225 main panel?

on his 200 amp main panel it is rated 225 max.but it is still a 200 amp panel.

 

[JBurgess]

What brand is this 225 main panel?

Probably a cutler-hammer.

 

[kool55]

Yes, it is a Cutler Hammer. Why do I need a disconnect at the sub with my setup? The main panel is 60 ft. away.

 

[Norcal]

Yes, it is a Cutler Hammer. Why do I need a disconnect at the sub with my setup? The main panel is 60 ft. away.

Because it is in a seperate structure, a main is required.

 

[kool55]

Not to sound stupid but what is the reason for making lug type panels if I need a disconnect? I would have used a main breaker sub panel. I read the label on the main and can't find max stab amps listed.

 

[JBurgess]

A main breaker (disconect) would not be required for an attached garage or other subs in the house.

 

[kool55]

But my main and sub is in the same room[shop].

 

[JBurgess]

I think there is some confusion. I thought you had a detached garage. If the Garage is attached, then a main is not required in the sub. If the Garage is detached there needs to be a main disconect for the garage usally the cheapest way is a main breaker panel. If there is a main disconect for the detached garage, then the subpanels could be MLO.

 

[kool55]

It a detached shop with its own meter and power supply. The meter is on the outside of the wall feeding directly thru to the main panel.I put the sub in on the far side to feed all the machines I set up over there.

 

[Aceman]

Your setup sounds fine.

 

[SiGmA_X]

This thread has gone a bit OT already, and right toward what I need info on.

I have a freestanding shop with a 200amp, using a Siemens main service panel. Meter is on other side of the wall, comes into the main panel, and it has a 200amp disconnect. I am going to run a 100amp subpanel across the shop (about 25ft) for machines. It seems to be the best way to do things here.

My question is which wire should I use? I am getting so much conflicting info, from tons of threads on here and other forums... I've looked through at least 100 threads, with many different "this is code" statements. As I understand it, I want to go with 2-2-2-8CU or 1-1-1AL-8CU, right? Please point me in the right direction!

Roman