bark
Member
- Location
- Washington
Can I get 2 #4's and 3#8's copper in 3/4" emt or pvc? I just realized today that I lost my code book. Have to put a new furnace in the house. Thanks
# of conductors in a 3/4" conduit
- Thread starter bark
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mdshunk
Senior Member
- Location
- Right here.
Re: # of conductors in a 3/4" conduit
Assuming you mean THHN... those conductors have a cross sectional area totalling .2746 square inches. That would mean 1" EMT or PVC40. That seems like a weird combination of conductors to me.
Assuming you mean THHN... those conductors have a cross sectional area totalling .2746 square inches. That would mean 1" EMT or PVC40. That seems like a weird combination of conductors to me.
jeff43222
Senior Member
- Location
- Minneapolis, Minnesota
Re: # of conductors in a 3/4" conduit
I've never encountered a furnace that required that kind of wirepower. What kind of furnace is it?
I've never encountered a furnace that required that kind of wirepower. What kind of furnace is it?
bark
Member
- Location
- Washington
Re: # of conductors in a 3/4" conduit
residential, one 60 amp breaker and one 30 amp breaker with one #8 for the ground. Single phase 240 volt.
residential, one 60 amp breaker and one 30 amp breaker with one #8 for the ground. Single phase 240 volt.
davedottcom
Senior Member
Re: # of conductors in a 3/4" conduit
Is 60 & 30 the Maximum Overcurrent sizes?
What's the Min. Circuit Ampacity for these units?
You might be able to run smaller conductors.
Is 60 & 30 the Maximum Overcurrent sizes?
What's the Min. Circuit Ampacity for these units?
You might be able to run smaller conductors.
bark
Member
- Location
- Washington
Re: # of conductors in a 3/4" conduit
I assume that the breakers in the furnace are maximum over current protection. I haven't seen the unit yet, but just wanted to get ready for it. It will be here Wed or Thurs. I have 1/0 al at the old furnace now, but it's under the house and would like copper to the unit instead of installing a sub-panel then short circuit runs to the furnance, being it is under the house. But with the price of copper now, and I'm buying material retail, I might go with the sub-panel. I think the furnace is 15kw. I haven't done residential for 26 years, so I'm a little rusty in that part.
I assume that the breakers in the furnace are maximum over current protection. I haven't seen the unit yet, but just wanted to get ready for it. It will be here Wed or Thurs. I have 1/0 al at the old furnace now, but it's under the house and would like copper to the unit instead of installing a sub-panel then short circuit runs to the furnance, being it is under the house. But with the price of copper now, and I'm buying material retail, I might go with the sub-panel. I think the furnace is 15kw. I haven't done residential for 26 years, so I'm a little rusty in that part.
davedottcom
Senior Member
Re: # of conductors in a 3/4" conduit
Don't forget 240.4(B) allows a 60 amp breaker (Next standard breaker size) on #6 NM as long as the min. circuit ampacity is 55 or less.
And a #10 EGC is all you need per 250.122.
Since you lost your book:
240.4(B) Devices Rated 800 Amperes or Less The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used , provided all of the following conditions are met:
(1) The conductors being protected are not part of a multioutlet branch circuit supplying receptacles for cord-and-plug-connected portable loads.
(2) The ampacity of the conductors does not correspond with the standard ampere rating of a fuse or a circuit breaker without overload trip adjustments above its rating (but that shall be permitted to have other trip or rating adjustments).
(3) The next higher standard rating selected does not exceed 800 amperes.
240.6 Standard Ampere Ratings
(A) Fuses and Fixed-Trip Circuit Breakers The standard ampere ratings for fuses and inverse time circuit breakers shall be considered 15, 20, 25, 30, 35, 40, 45, 50, 60 ...
Table 250.122 Minimum Size Equipment Grounding Conductors...
60 Amps: #10 copper
My guess is you could probably get away with pulling 2 # 6's and 3 # 10's, but I'd have to know the Min. Cir. Ampacities first.
Don't forget 240.4(B) allows a 60 amp breaker (Next standard breaker size) on #6 NM as long as the min. circuit ampacity is 55 or less.
And a #10 EGC is all you need per 250.122.
Since you lost your book:
240.4(B) Devices Rated 800 Amperes or Less The next higher standard overcurrent device rating (above the ampacity of the conductors being protected) shall be permitted to be used , provided all of the following conditions are met:
(1) The conductors being protected are not part of a multioutlet branch circuit supplying receptacles for cord-and-plug-connected portable loads.
(2) The ampacity of the conductors does not correspond with the standard ampere rating of a fuse or a circuit breaker without overload trip adjustments above its rating (but that shall be permitted to have other trip or rating adjustments).
(3) The next higher standard rating selected does not exceed 800 amperes.
240.6 Standard Ampere Ratings
(A) Fuses and Fixed-Trip Circuit Breakers The standard ampere ratings for fuses and inverse time circuit breakers shall be considered 15, 20, 25, 30, 35, 40, 45, 50, 60 ...
Table 250.122 Minimum Size Equipment Grounding Conductors...
60 Amps: #10 copper
My guess is you could probably get away with pulling 2 # 6's and 3 # 10's, but I'd have to know the Min. Cir. Ampacities first.
davedottcom
Senior Member
Re: # of conductors in a 3/4" conduit
Min. Cir. Amps determines the size of wire.
Max. Overcurrent determines breaker size.
Just be sure to use the 240 Volt specs!
Forget KW ratings! Tha factory will calculate the Min Cir Amps and Max Overcurrent for you!
Min. Cir. Amps determines the size of wire.
Max. Overcurrent determines breaker size.
Just be sure to use the 240 Volt specs!
davedottcom
Senior Member
Re: # of conductors in a 3/4" conduit
Wait a sec! 15 KW! looks like it will be over 55 amps!
Nevermind!
15,000 / 240= 62.5 plus the blowers etc...
Sorry, you probably will need the #4's, but #10 for the 30 amp unit and EGC should work.
.0814
.0814
.0243
.0243
.0243
-----
.2357
40% 0f a 3/4" EMT is .213
Still no good
Hopefully it's not a 15KW!
[ January 01, 2006, 08:22 PM: Message edited by: davedottcom ]
Wait a sec! 15 KW! looks like it will be over 55 amps!
Nevermind!
15,000 / 240= 62.5 plus the blowers etc...
Sorry, you probably will need the #4's, but #10 for the 30 amp unit and EGC should work.
.0814
.0814
.0243
.0243
.0243
-----
.2357
40% 0f a 3/4" EMT is .213
Still no good
Hopefully it's not a 15KW!
[ January 01, 2006, 08:22 PM: Message edited by: davedottcom ]
bark
Member
- Location
- Washington
Re: # of conductors in a 3/4" conduit
The hvac contractor thought it was at least 15kw. I thought it was 20 kw. I'm not to sure if adding a subpanel under the house is legal. It won't be gfci but just for the hvac equipment, a light,and a recepticle.
The hvac contractor thought it was at least 15kw. I thought it was 20 kw. I'm not to sure if adding a subpanel under the house is legal. It won't be gfci but just for the hvac equipment, a light,and a recepticle.
macmikeman
Senior Member
- Location
- Planet macmikeman
Re: # of conductors in a 3/4" conduit
Would you mind if I stole this from you?
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