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Feedback on subpanel, heating circuits, wiring diagram, parts list

Feedback on subpanel, heating circuits, wiring diagram, parts list

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  #1  
Old 11-18-13, 07:53 PM
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Feedback on subpanel, heating circuits, wiring diagram, parts list

Hi folks.

Really appreciate the help on this forum! I'm about to go finish getting all supplies in prep for installing a subpanel, heaters, lights, and outlets. I've done electrical before, but not a subpanel. An industrial electrician friend will be helping this weekend, but wanted to get your thoughts specific to residential code, and make sure I don't forget essential items.

The plan:

Install subpanel in detached yurt, 200' distance from 200A service panel. Run 7.5kW of radiant cove heating, plus minimal lighting and general outlets. See diagram -- note that grounds and neutrals are not generally shown. Neutrals in 240V circuits are not switched. Ground wires connect everything.

* The main run of feeder is Al THWN in 1.25" PVC, 18" underground.

* The feeder is on a 60A breaker on the service panel, comes into the 100A main lug subpanel backfed into a 90A breaker in the first breaker space with a hold-down device.

* Ground wire connects ground/neutral bar of service panel with ground bar of subpanel. Ground bar of subpanel connects to two grounding rods 7' apart. Ground and neutral of subpanel are disconnected.

* The heaters and one run of lights are Cu THHN in 3/4" flex.

* The other run of lights is 14/2 flex.

* And the outlets are 12/2 NM Romex stapled to joists (not across them) under the floor platform (installed via crawlspace).

* Two outlets are flush with the floor facing up, and one is outside in outdoor enclosure.

* The heaters are controlled by a line voltage thermostat, which controls all three circuits using 15A (resistive) 3PDT ice cube relay with 240V coil. Each heater is also controlled by a 2-pole switch.

Main questions:

1) Is there anything in this layout you're concerned about? Code or safety.

2) What size enclosure do I need for the ice cube relay, and how do I attache a DIN rail etc.?

3) Confirm that it's code & wise to use #4 neutral in this application. Only significant continuous load is the heaters, which will balance on the hots because they are 240V, so neutral should be very low.


Thanks everyone!
 
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  #2  
Old 11-19-13, 06:36 AM
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The main run of feeder is Al THWN in 1.25" PVC, 18" underground.
Aluminum THWN is usually a special order. I suspect you'll have an easier time finding Type XHHW or Type USE conductors.

The feeder is on a 60A breaker on the service panel, comes into the 100A main lug subpanel backfed into a 90A breaker in the first breaker space with a hold-down device.
I am certain the #2 aluminum conductors are too big for the lugs on a 60 amp breaker, I know they are marginal in a 90 amp breaker. You may have to splice the #2 conductors to a smaller size in a junction box adjacent to the main service panel or possibly use pin connectors to reduce the size appropriately to fit the 60 amp breaker.

Two outlets are flush with the floor facing up, and one is outside in outdoor enclosure
You will need floor boxes designed for a wood floor for the floor receptacles along with the appropriate trims. These should be readily available from most supply houses.

And the outlets are 12/2 NM Romex stapled to joists (not across them) under the floor platform (installed via crawlspace).
I believe these cables will have to go through holes bored through the floor joists, not under them. Since this is a crawl space, I may not be correct on this one, but my opinion is bored holes.

Ground wire connects ground/neutral bar of service panel with ground bar of subpanel. Ground bar of subpanel connects to two grounding rods 7' apart. Ground and neutral of subpanel are disconnected.
I would just use one ground rod unless the AHJ requires you to use two. #6 copper, bare stranded is my preference for the GEC.
 
  #3  
Old 11-19-13, 11:36 AM
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Thanks for the feedback!

Aluminum THWN is usually a special order. I suspect you'll have an easier time finding Type XHHW or Type USE conductors.
Shoot, yes of course, I meant XHHW (priced pretty reasonably at Platt).

I am certain the #2 aluminum conductors are too big for the lugs on a 60 amp breaker, I know they are marginal in a 90 amp breaker. You may have to splice the #2 conductors to a smaller size in a junction box adjacent to the main service panel or possibly use pin connectors to reduce the size appropriately to fit the 60 amp breaker.
Thanks, this is great experience-based info! I ordered the breaker online, and thought it said it would handle down to 1/0, but doubtless misunderstood. So I should splice to #4 (Cu or Al?), or use pin connectors? Is there a preferred approach -- is this considered substandard? Or should I try to go to a 100A breaker on either end (which I think is still to code by wire size, and the voltage drop over the long 200' run won't make a difference in practice since actual use will just be ~35A continuous at peak.)?

You will need floor boxes designed for a wood floor for the floor receptacles along with the appropriate trims.
Oh, is that a code thing? I figured it was just aesthetic -- and expensive. I was thinking of using a regular receptacle (which I have a bunch of from previous project) and using those little plastic inserts to protect from dust. Otherwise might need to revert to vertical wall box -- can I use a regular enclosure (like I would use inside a wall) when it's against the wall but not surrounded (ie. attached to the wood lattice on the back with conduit coming up from the floor)?

I believe these cables will have to go through holes bored through the floor joists, not under them.
I was thinking about that, and was wondering how much a small 1/2" hole might compromise strength of joist? Should I use those metal reinforcing plates? (These are 2x6's) I agree that it's slightly safer to bore holes in the case that someone uses the crawlspace for storage.

I would just use one ground rod unless the AHJ requires you to use two. #6 copper, bare stranded is my preference for the GEC
Local electrician friend indicates two ground rods are preferred around here, and doesn't seem like much more expense/work. Any preference re: galvanized vs. Al vs. Cu rod?

Thanks again!
 
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