Electrical Question - Cable Fill

[crokett]

My electrical service at home is the main panel sits next to the meter box. The existing main has 6 breakers and no main shut off. By code, with no main shut off I am allowed a maximum of 6. I will be replacing the panel with one that has a main and can handle more circuits. I can't replace it in place because the heat pump is in the wrong spot and it will cost 400 bucks to move the heat pump. So I am going to put the new panel on the other side of the meter then use the existing one as a junction box and extend the 6 circuits to it. The 6 circuits are 2 with 2-2-4 aluminum, 2 10/2 copper 1 12/2 copper and 1 more that I think is 12/2 copper. My question is on cable fill for the conduit over from the old panel to the new. I assumed all the smaller copper to be #10 for the calculation so figured it at 4 #2 conductors and 8 #10. As near as I can tell, 2" conduit will work for this application. I would run everything through the conduit unsheathed. Also, rather than running elbows from the top of the old panel to the top of the new, there is just room for 2" conduit out the side of the old box, straight across to the new panel above the meter. As long as the meter cover can open, are there any clearance requirements for the conduit? It would be just about sitting on top of the meter box.

thanks

 

[Gotcha6]

Let me first say this: I am not an electrician. I have been in construction for 40+ years & have been involved with many service upgrades as you are contemplating. I make these comments & recommendations based on those successful experiences only.
You would be better served to supply your old panel with a single line set and breaker assembly from the new panel with wire sizes equal to the feeders now serving it from the meter taps. It would eliminate a lot of unnecessary splicing and make the job much simpler and faster. The new panel only needs to be large enough to supply the existing panel and any additional connected loads with a safety factor of 1.25 i.e. a 200 amp panel can only handle 80% or 160 amps of CONNECTED load - not circuits. This is the most commonplace method of doing what you intend and is also the least inconvenient to accomplish.
As far as routing the conduit, you are allowed a maximum of 360 degrees of bends in a run from point to point. You may achieve this using what is known as an "LB" 90 degree bend if necessary, but as long as you have your conduit behind the panelcover & it doesn't interfere with the existing circuit feeders, go for it.

 

[Travis Porter]

I too will say I AM NOT AN ELECTRICIAN.

To me, Dennis makes a LOT of sense and that is exactly what the electricians did at my parent's house.

If you have decided to go the route you are suggesting though, you have to take the type of wire, size of it, and then add it all up and check the NEC code book to make sure you do not exceed the requirements.

As for the conduit placement, as long as it isn't touching, and there is appropriate clearance to work in the panel below it, I do not believe you will have any code issues.

 

[crokett]

You would be better served to supply your old panel with a single line set and breaker assembly from the new panel with wire sizes equal to the feeders now serving it from the meter taps. It would eliminate a lot of unnecessary splicing and make the job much simpler and faster. The new panel only needs to be large enough to supply the existing panel and any additional connected loads with a safety factor of 1.25 i.e. a 200 amp panel can only handle 80% or 160 amps of CONNECTED load - not circuits. This is the most commonplace method of doing what you intend and is also the least inconvenient to accomplish

So what I am hearing is move the feeders from the meter base to the new panel, install a 200A breaker in the new panel and then run feeders appropriate for 200A back to the old panel? That is an interesting thought and I agree it is much simpler. Plus I can install a smaller and cheaper panel. Also, what is 'connected' load? The max load I expect to be running at any one time? I would think that is what it is since the existing main panel is rated at 200A and has a lot more than that in it if you total up the breaker sizes.

 

[Gotcha6]

If you have a 12 month history of your power bills and you have a demand type meter the Inspection Dept. will accept the highest demand load in that period as a 'baseline connected load', meaning how many appliances, lights, etc. you hay have had on simultaneously.
If your old meter & panel is a 200 amp and your new on is larger you will need to upgrade to a "CT" type system which uses induction rings on the line feeders and offsets the meter from the feeders. How large is your new main breaker? 300amp? 400 amp is usually the max you'll see on homes smaller than a McMansion.

 

[crokett]

Something about your suggestion was bugging me and I figured out what it was. The reason I have to extend the circuits over to the new main is the heat pump is in the wrong place. I was originally just going to replace the panel but I can't unless I move the heat pump. So I am back to extending all 6 circuits.

 

[Gotcha6]

Why was the heat pump put there - and by whom? NEC has requirements on these sorts of things.

 

[crokett]

It was put there by who ever installed it in 2003. The house is 30 some years old. I suppose I could look it up. The inspector didn't seem surprised that they'd done that. I had a question on something else and had a guy from the power company out this morning. While he was there he looked at it and said he would either pay the money to move the heat pump or instead of adding a 2nd panel he would replace the meter base with a new combo meter/base panel and then extend my circuits into it. His reasoning (and something I was concerned about already) is that the SE from the poco and the feed to the new panel woudl both be in the same corner of the box and routing cables would be tricky if not impossible. Now to replace the meter base I'd have to dig up the conduit, take it off and cut it down since the new meter base would be taller than the old and have to be lowered to make the SE from the poco long enough. So I guess the question is, which way is easier to do? Seems to me just adding a new panel would be and I live with routing the wiring. Anyway, here's a pic of the current setup.

 

[Gotcha6]

Don't know how strict they are in your county, but in the 'Great State of Mecklenburg' where I do most of my work, they usually require projects of this magnitude be done by a licensed electrician rather than a homeowner. You will need to have the poco disconnect your service at the transformer & then they usually handle the reconnection of the feeder wires after you have relocated the new meter/panel. They usually do not do this reconnect until authorized by the Inspector after he has approved your new service installation, so be prepared to be without power for that length of time. On commercial projects we do this sort of thing at night after everyone has gone and poco will reconnect only if the Inspector has coordinated the work and 'pre approves' the installation. He has the authority to have it disconected if he feels the work is not acceptable. A good time of year to be doing it since the weather has moderated & you could put your fridge/freezer on a generator for awhile.
Good luck.

 

[terry1166]

The problem you will run into by trying to install all of the existing circuits in one conduit run is that the National Electrical Code requires de-rating of the listed current rating of conductors once 4 or more current carrying conductors are installed in a conduit (unless the total length of the conduit run is less than 18"). For instance, for 4 to 6 current carrying conductors, the code states the listed current rating is to be reduced to 80% of that listed. For an example, if you have a #10 conductor normally rated at 30 amperes connected to a 30 ampere circuit breaker, the de-rated conductor would be approved for 24 amperes and cannot be connected to a 30 ampere circuit breaker. You would have to run #8 conductor instead of #10.

If you currently have a standard residential type meter, you cannot get a record of demand. The monthly KWH usage total gives no indication of the existing demand load.

I would suggest that instead of conduit, consider using an electrical raintight trough to run the existing circuits back to the old panel that you're making into a junction box. A properly sized trough would require no derating of conductors. The wiring trough would be installed above the new panel, the meter enclosure and the existing panel. You would then install short conduit nipples from the bottom of the wiring trough to the top of the new panel and the existing panel that you are making into a junction box. These short 2" or 3" nipples would be sized based on NEC requirements and due to the short length, no conductor de-rating factors will apply. If you are permitted to do this type of work in your city/county without be a licensed contractor, the electrical inspector should be willing to help you size the conduit nipples and the wire trough. For the number of circuits you listed, I'm guessing (because I don't have a code reference handy) that you would probably only need a 4" X 4" trough with the length being as required to get from above the new panel to the old enclosure. Raintite troughs can be purchased in several lengths from electrical supply houses. The electrical inspector should also be willing to help you with advice on the grounding electrode connection changes that will be required.

If you are not allowed to perform this type of electrical work in your city/county without a contractors' license, hire a licensed contractor. You will more than likely not be able to do this work without being noticed due to the fact that the meter seal will have to be cut and the meter removed to kill power to the existing panel and to make the new service conductor connections.

Terry Davis

 

[BobcatBob]

The 6 circuits are 2 with 2-2-4 aluminum, 2 10/2 copper 1 12/2 copper and 1 more that I think is 12/2 copper. My question is on cable fill for the conduit over from the old panel to the new.

I know this wasn't you question but if you have two 2-2-4 al circuits, then you must have 2 subpanels in you house somewhere. Would it be possible to use one of them for what you want to do. If I added this correctly, you already have 280 amp circuits in this existing box. Is the meter you have a 200 amp meter or are you going to have to replace it anyway?

 

[crokett]

Sorry for the delay in the replies. I've been dealing with a few things.

1. I am allowed to do my own work. I asked the the inspector. I've installed panels before but at someone else's direction. Inspector did suggest I at least pay an electrician to consult and/or check my work. I've done that.
2. Inspector said 2" conduit but said keep the run short, under 24" if possible. I am not sure I can do that. It will be closer to 28" I think. I know about derating of the conductors. I assume that is why he said that. I will look into a trough. I did not know about those. It will probably make it easier to pull all the wiring.
3. I will have the poco disconnect the power at the pole. I know they won't put the power back on until it passes inspection.
4. 2 90A circuits each wired with 2-2-4. One goes to a sub in the basement, other goes to heat, well the air handler for the heat pump anyway. I think the house originally had electric heat. I could probably downsize the breaker and the wiring used to extend the circuit but I just want it to pass inspection.
5. For the equipment ground in the existing panel I will run a #4 ground from ground bus on the new panel back through the conduit to the old. The existing grounds/neutrals will stay in the old panel. The #4 is as per an electrician - it is equal in size to required ground for the largest conductor.
6. For the ground rod I either have to put the existing all the way down (about 18" is out of the ground) or add a second one. I plan to add a new one, would rather not start and discover I can't put the old all the way down for rocks, etc.