Sub-Panel questions

[Bruce King]

Lots of errors are made with sub panels. I inspect houses for a living and see it all so here is some advice.....

Sub Panels must be fed with a 4 conductor cable. The neutrals and grounds must be on seperate busses. This is known as "floating neutral". Only the ground bus can be bonded to the metal box with the (usually)green screw. Also the neutral wires must be connected seperate under each screw, no double tapping allowed on hots or neutrals. The exception for hot wires is on the breakers designed for two wires. The way to tell if it is designed for two wires is that the wires do not touch each other when installed on the breaker. FYI, the correct term is "panel" but I like sub panel since everyone knows what they are. Technically you only have "main panels" or otherwise known as "service equipment" and then all else is just a "panel". The only place where the neutrals and grounds are connected together is at the service equipment or main panel.

[Jay Maiers]

Jay,
Are the lugs compatible with aluminum wiring?
Tom

I certainly hope so. It appears that the inbound power is on aluminum. I can't really see any wire around the two main lugs, but the third cable that I can see is aluminum.

Before you use aluminum wiring do a Google search for "aluminum wiring dangers"...

Yeah, I've done a bit of reading on that subject; my understanding is that you have to use some sort of conducting compound where the wire joins the lugs, and check the torque values once in a while to make sure that the wire expansion has not loosened the connection.

However, as short of a run as this is, copper won't break the bank.

Dan / Tom, I'm one grounding slot shy of putting two big breakers in the existing box. I don't like the idea of doubling up the ground or neutral connectors, and it seems silly to add ground and neutral bars to the existing panel, plus add the extra panel. However, it's a valid point, and I'm re-thinking things right now. After taking a careful look, I've got a LOT more planning to do. One thing that I am sure of is that I do want an additional panel. I like the idea of segregating the shop / downstairs power for safety (lockout) reasons as well as the ability to run power and work on things without shutting down the main power panel. It just makes good sense to me. I know it'll cost a couple of hundered bucks to get the panel in and working, but I think it will be worth the money and hassle in the end.

[Jay Maiers]

After thinking about it, I don't think the house will allow more than another 50-60A during the summer. The house has (2) AC Units with a 70A breaker, plus the normal house stuff.

During the winter (gas fired heat)If I fire up the kiln (60A breaker) plus the lights in the basement (10-15A, depending on how many lights I turn on), plus a small tool and dust collection, I'll probably be over 60A. Do I need 100A? No. 75-80 would probably suffice. I picked 100 to keep from flipping breakers or starving any point of the system. I was stuck for way too long in a garage shop with inadequate power. I can't tell you how many times the compressor kicked on right in the middle of a cut, tripping the breaker


Bruce, the panel that I picked has a thick bonding wire stretched across the breaker mounts, and screwed into the bars. I'm assuming that I just have to cut that wire in order to seperate the two.

As soon as I can figure out who has inspection jurisdiction (county or city) and which office to call, I'll be able to get some more concrete info. Until I know if I can mount that panel upside down or if I am really allowed to bring the power in through the bottom, I'm sort of stuck in limbo. Not really a bad thing since I still have boxes of stuff all over the house, waiting patiently (along with my wife) for me to put them away

Thanks everyone!

[Rollie Meyers]

Bruce, the panel that I picked has a thick bonding wire stretched across the breaker mounts, and screwed into the bars. I'm assuming that I just have to cut that wire in order to seperate the two.

As soon as I can figure out who has inspection jurisdiction (county or city) and which office to call, I'll be able to get some more concrete info. Until I know if I can mount that panel upside down or if I am really allowed to bring the power in through the bottom, I'm sort of stuck in limbo. Not really a bad thing since I still have boxes of stuff all over the house, waiting patiently (along with my wife) for me to put them away

Thanks everyone!

The only thing preventing mouting a panel "upside down" is if there was a vertically mounted main breaker because the "ON" position has to be up, which is why most resi panels have been redesigned w/ sideway's operating main breakers.

Do not cut the bonding between neutral bars, buy a ground bar kit instead,a split neutral is for ease of wiring.

[Dan Friedrichs]

Also the neutral wires must be connected seperate under each screw, no double tapping allowed on hots or neutrals.

I thought multiple ground wires under screws was allowed. Clearly you can't put both the neutral and ground under the same screw on a sub panel, but you can put multiple grounds under the same screw.


Jay - if you're only one ground lug shy in the main panel, you should consider just moving some of the existing ground wires out of their own spots and making them share a spot with other existing grounds.

[Don Jarvie]

Jay,

A few thoughts, if your worried about not having enough amps then have you service into your house upgraded to 200 amp. This will provide plently of power.

Instead of a subpanel, put in a full panel with a 100A breaker to power the shop/kiln. All you need is 2 slots in your main panel for a 100 A breaker. The beauty of a full panel is you can have plently of slots to run lines throughout your shop. Sub-panels limit you to 6 or so slots.

It's probably worth the money to bring in an electrician and upgrade your system especially since the kiln pulls all that power.

[John Coloccia]

re: multiple neutrals under the same screw
Under certain conditions, that MAY be allowable if I'm remembering correctly. I forget exactly what criteria exists for that. As a general rule, though, it's not allowable.

You can put up to 3 ground wires under together provided that they are the same gauge and that the panel is rated for it.

That's my understanding.

I believe part of the reasoning for these rules is to prevent a situation where a current is forced through the screw, instead of the bar, or where a 30A ground fault coming in through a 10AWG wire travels through the 14AWG wire it's bundled with. That would be VERY bad. It's always a VERY good idea to refer to the NEC when doing any wiring as these guidelines are usually in place for a good reason.

[Dan Friedrichs]

re: multiple neutrals under the same screw
Under certain conditions, that MAY be allowable if I'm remembering correctly. I forget exactly what criteria exists for that. As a general rule, though, it's not allowable.

You can put up to 3 ground wires under together provided that they are the same gauge and that the panel is rated for it.

Yeah, John - you're right. If the box is rated for it, multiple grounds can be put under a single screw, but not multiple neutrals. I appologize for misstating that in my earlier post, and corrected it.

[Joe Wiliams]

Regarding side by side panels & the covers (having the panels in adjacent bays).

Is there a way to make this work?

[John Coloccia]

Yeah, John - you're right. If the box is rated for it, multiple grounds can be put under a single screw, but not multiple neutrals. I appologize for misstating that in my earlier post, and corrected it.

No biggie. Multiple eyes on a problem has picked up many boo boos in my line of work...usually mine. LOL.

[Jay Maiers]

Regarding side by side panels & the covers (having the panels in adjacent bays).

Is there a way to make this work?

The original panel has a narrow door in the center of the box. If the new panel had the same size door, it wouldn't be a problem. Unfortunately, it's a wide door, so I'm going to mount the new panel on the right side of the old one, and upside down so that it opens away from the existing panel.

[Brian Cover]

1) Am I allowed to run power out through the bottom of the existing panel, throught the stud, in through the bottom of the new panel, and up to the main breaker lugs at the top? (I'm planning on using 2-2-2-4 Aluminum for this connection)

Why not just drill a hole in the side of each panel and bridge them with 1.5" conduit? That is much easier than trying to route wires through a hole in the wall, through a stud, and back into a panel.

That's how I install panels.

[Greg Woloshyn]

Quick question: I have a sub panel I'm installing with a 60 amp breaker that is going to be connected to an existing sub panel in the house that is only fed with 50 amps. Will I still be able to install a 60 amp breaker for my new panel?

[Jay Maiers]

Why not just drill a hole in the side of each panel and bridge them with 1.5" conduit? That is much easier than trying to route wires through a hole in the wall, through a stud, and back into a panel.

That's how I install panels.

Not a bad idea, but the existing wiring (inside the main panel) would have to be removed and reconnected. there's next to no open space on that side of the panel. The other side is nice and open, unfortunately there's no room for the new panel without removing / changing the wall stud layout.