Subpanel wiring


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Old 11-05-08, 02:17 PM
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Subpanel wiring

Hi...Brand new to this forum and needing some help..I am in the process of building an addition on my house for a workshop..I have 200 amp service and a subpanel with a 30 amp breaker.....I am needing to put a 220 30 amp circuit in this subpanel for a electric heater for the addition which draws max of 20.8 amps...I also on this circuit have 5 20 amp circuits and 1 15 amp..this is in a garage so the circuits are for the lighting etc..

My question....Can I put a 30 amp circuit in this subpanel or do I have to put a larger amp breaker in the main box to power this subpanel..The wire from the main panel to the subpanel shows the following marks..
Type E Alloy X-E32071 (UL) 6-3 AL Would think this wire would handle a larger breaker..

Many thanks for replies..
 
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Old 11-05-08, 04:02 PM
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The answer will depending if this garage is attached or detached type.

For the conductor the # 6-3 AL is typeally used with 40 amp breaker is this cable is SER or other ? { it should have addtional marking on it }


Merci,Marc
 
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Old 11-06-08, 05:27 AM
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For some reason part of my post didnt print..Anyway it is actually a third stall on my attached garage which I am going to use as a workshop..
The marks on the wire to the subpanel are: Type SE Cable Style U Type XHHW CDRS 300V to Ground Triple E Alloy X-E32071 (UL) 6-3 AL....main concern is putting the 220 circuit into this subpanel with 30 amp fuse with the incoming wire also 30 amp....Many thanks..
 
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Old 11-06-08, 03:45 PM
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The #6 SE aluminum is okay to bump up to a 40A breaker if necessary provided that the subpanel itself is rated for at least 40A.
 
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Old 11-06-08, 09:38 PM
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Dang., I think we may be little too late here but you say SE cable right two hot conductor and netural ?

If the case the old code it used to be allowed but not the current code it have to be seprated anyway.

How long this cable run is ? and if easy to get into ?

If so you can get 6-3 SER cable this will have two hot conductors, netural conductor and grounding conductor { typcially the SER will have Black , Black with red strip or red , White or black with white stripe and finally bare alum conductor }

And the netural and ground it will be seprated all the subfeed appactions.

Merci,Marc
 
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Old 11-07-08, 05:48 AM
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It is SE and has 2 black and 1 ground...This was just rewired by a local electric company couple years ago and apparently passed inspection but dont know how close anyone looks at the wiring...

With the present 30 am to the subpanel am I going to have trouble adding a 220 to the subpanel with a 30 amp fuse??? The SE wire is hidden inside some finished rec room ceililngs and is approx 30 foot from the main panel to the subpanel..
My new furnace in the addition is approx 40 ft from the subpanel...If I cant use the subpanel for this 220 I could run the wire from the furnace around the other side of the house to the main panel which has the room...would be little over 100 ft total of wire to reach the box...Which way would you advise me to do it...Really appreciate the input and quick responses from this Forum...
 
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Old 11-07-08, 06:24 AM
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As stated earlier, you can swap out the 30 amp breaker in your main panel with a 40 amp one. Your sub panel feed is rated at 40 amp.

If your main panel and sub panel use the same type breaker, then you can just use the replaced 30 amp breaker in your sub panel.

But you have 5 20 amp circuits in your sub panel as well to power garage receptacles and lights. That would only leave you 20 amp or less in your garage, while the electric heater is running.

Up to you on what you want to do. Feeding the electric heater from your sub panel means you'd have to be careful of what you use out in the garage.
 
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Old 11-07-08, 06:46 AM
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Thanks...I think best way is to run the extra wire all the way to the main panel....Going to be running power tools etc in the addition and want it to be done right...

Appreciate all help..
 
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Old 11-15-08, 03:00 PM
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Exclamation You should be able to put a 30A breaker in a 30 A sub panel

Let me see if I understand your question.. You have a 30A sub panel with a 30 A breaker supplying it? the sub panel has 5 20A circuits and 1 15 A circuit. 6/3 is feeding the sub panel. Technically 6/3 wiring can handle 55 Amps. If the 30A breaker for the sub panel trips then replace the 30Amp breaker with a 40 or 50Amp breaker. Loads are derated for example if you added up the breakers in your main panel the sum is greater than 200A but not everything runs at once for example the AC unit and heat do not run at the same time etc. In your garage letís assume the heater runs all the time at 20.8A in theory you have 9.2 A remaining. This should be ample to run most power tools. I reality the heater probably only draws 8A - 12A once it's up and running. The 20.8A is probably for the initial current surge at startup.

The short answer put a 30A breaker in the subpanel and run 10 AWG wire for a dedicated heater circuit. Use your shop as you normally would if the breaker doesn't trip you should be ok. To make sure that it will not end up being a nuisance run the heater, a shop vac and as many power tools that you can run at once, if none of the breakers trip then your done.

That being said never ever replace a breaker with a higher amperage breaker without verifying the wire size is adequate to handle the current. I have seen wire glow like a heating element and melt off the insulation from an over current condition.
 
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Old 11-15-08, 09:25 PM
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Originally Posted by huffjohndeb View Post
Technically 6/3 wiring can handle 55 Amps.
John, the poster said that he had #6 aluminum cable which has a maximum ampacity of 40A. You posted the ampacity of #6 copper cable.
 
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Old 11-16-08, 05:44 PM
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Good point I missed the fact that the wire was Ai not Cu big difference.

I would stick with the 30A service and see what happens. I would hesitate to advise a breaker change unless proper termination tecniques and materals are used i.e. device is suitable for aluminum and the proper anti-oxidant grease is used.

Back to my original point the heater is rated at 20.8A max. I would venture to guess that the heater could be protected with a 20A circuit breaker used with 10 AWG wire. If I had to buy a breaker I would buy a 30A breaker.
 
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Old 11-17-08, 07:47 AM
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Code requires 125% oversizing of conductors and breakers for fixed-in-place heaters; therefore the circuit must be designed to support 26A. The next standard breaker size is 30A, so 30A breaker and #10 wire is required for this heater.
 
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Old 11-17-08, 11:22 AM
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Thanks a lot for all the information....I ended up running the 10 cable all the way to the main electrical box just to be safe..Ended up running about 110 feet through 3 rooms and jog through a closet but all is working well...I would rather have the power in the subpanel to run power tools etc than worry about tripping breakers with the heater running along with everything else..

Very impressed with all the help you people give on this forum..I will not hesitate to contact you again if I have any questions in the future..

Again many thanks for the interest and advise..
 
 

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