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Hmmm... 6/3 to panel in garage...

#1
07-24-07, 09:38 AM
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Hmmm... 6/3 to panel in garage...

I've got a run of 6/3 (copper) going from a 60 Amp Double Pole breaker in the house to a sub-panel in the garage. The sub-panel is configured with two hot "poles" (each side servicing on side of the box), and then naturally a neutral and a ground pole along the side of that...

My question for you is this, isn't 6 Gauge rated for 50 Amp, not 60?

Also, when you add up the total breaker amp on each side, they exceed 60 amps (for example, on the left side there are 4 20 amp breakers, running via 10 Gauge to 4 different receptacles (10 gauge, servicing a 20 amp breaker, I know is fine). But is the rest of this right?

Any insight you can give would be much appreciated.

Thanks!

#2
07-24-07, 09:42 AM
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Some questions first:

Is this an attached or detached garage? Is this a cable assembly of wires, or is it individual wires? Are there three or four wires?

Each hot wire into the sub panel does not serve a side of the panel. Every other breaker is served by the same hot wire. This allows two adjacent breakers to be used to make 240 volts.

The sum of the individual breakers means nothing. First of all, you would want to compare against 120, not 60, and even then it means nothing.

#3
07-24-07, 09:59 AM
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This is a detached garage. The feed is buried (UF) 6/3. This means that there are a total of 4 wires inside the sheathing... 2 Hot, 1 Neutral and 1 Ground (Red-Black-White-Bare).

Thank you for the clarification on the sum of breakers not mattering...

on the left side, working from top to bottom:

15
15 (This is a tandem breaker with two 15s)
------------------------
20
20 (This is a tandem breaker with two 20s)
------------------------

on the right side, working from top to bottom:

15
-----------------------
20 (Dedicated 120 Air Conditioning Receptacle)
-----------------------
30
30 (This is a double pole breaker, full size -- it services the electric base-board heat (never used @ same time as A/C Unit)
-----------------------

Is this sufficient? What should I know?

Thanks for the quick reply Bob, it is very appreciated.

#4
07-24-07, 10:03 AM
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The run of the 6/3 is 40 feet.

#5
07-24-07, 10:35 AM
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> isn't 6 Gauge rated for 50 Amp, not 60?

Type UF-B #6/3 is rated for 55A. In this case, code allows you to "round-up" to the next standard breaker size of 60A.

> naturally a neutral and a ground pole along the side

There should be separate neutral and ground buses in a subpanel which have been isolated by removal of the bonding screw or strap (unlike a main panel where neutral and ground are combined). It's unclear from your description if they are separate or combined.

Also, you should have a bare #6 copper wire running from the subpanel ground bus to a 5/8" x 8' copper-clad ground rod driven into the earth.

> add up the total breaker amp on each side, they exceed 60 amps

That's okay, because it is extremely unlikely that all circuits will be running at 100% at the same time. As long as the typical simultaneous load does not exceed 60A, the subpanel is fine as is.

#6
07-24-07, 11:08 AM
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Thanks. Yes, the two buses are separate and the rod, etc. are all fine.

So, here is my next question... say I needed to use a piece of equipment that was a 4500 watt, 240 volt immersion heater... could this be done, say with the heat on in the building at the same time? Or are we asking for trouble?

#7
07-24-07, 11:19 AM
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That only 18.75 amps so you should be fine. I will be corrected if I am wrong.

4500 / 240 = 18.75

#8
07-24-07, 11:24 AM
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You haven't told us how much power the heater needs. However, 30 amps at 240 volts and 20 amps at 240 volts is still less than 60 amps at 240 volts.

#9
07-24-07, 12:13 PM
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The only information I have at this time is that it is a 4500 Watt immersion heater and requires 240.

What information, exactly, are you looking for? Is the calculation made by HotinOKC correct? If so, would I be correct in thinking that a double-pole 20 amp breaker would be appropriate, done with 10/3 copper. Hardwired from the t-stat of the heater to the panel.

#10
07-24-07, 12:23 PM
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However, the calculation shown is correct, but it does NOT address the size circuit needed.

#11
07-24-07, 12:54 PM
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If it ok with you, let's assume the baseboard draws the maximum allowed by the breaker. Which in this case is a double-pole 30 Amp.

Spoke with Watlow, the mfg. of the immersion heater and the draw is in fact 18.75 as indicated in this thread. The recommend a 20 Amp double-pole breaker wired with 10/3. (Distance from panel to immersion heater is under 15 feet).

I just want to thank you again for taking the time to work this out with me.

Thanks again,
Pete

#12
07-24-07, 01:00 PM
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> 4500 Watt immersion heater and requires 240.

This should use 18.75A max. This may require 30A breaker and #10/2 or #10/3 based on its intended use or manufacturer's instructions.

> 30A baseboard heat

If this was installed per code, there should be no more than 24A of heaters on this circuit.

This leaves you with 42.75A in-use which should be okay on your 60A panel assuming not too much else is running at the same time.

#13
07-24-07, 01:11 PM
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Yeah... that is what I thought you'd say... cutting it kinda close if you ask me.

Hmmmm... Now I have to decide if we should run another 60A line out there or not. I hate trench digging.

#14
07-24-07, 01:35 PM
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You can't run another 60 amp line out there. You can upgrade the current line to be 100 amps (or 80 or 150 or 200), but you cannot add a second line.

Only one circuit allowed to an out building.

#15
07-24-07, 01:51 PM
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I don't think it's that close. The remaining ~15A @ 240V is quite a bit of power. That's plenty for lighting and some tools. Plus, you have to consider that the baseboard heaters cycle on and off periodically.

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