70 A subpanel addition

[joshgarcia]

Hey fellas, do you see any issue i may have in the following scenario: I have a 100 A breaker mounted out on a pole that feeds the house panel. I want to add a 70A subpanel out on the pole to provide power to a couple of 15A receptacle circuits outside...? I would most likely tap off of the load side of the 100A breaker.

thanks

 

[augie47]

Aside from possibly of needing a load calculation, the biggest obstacle is that the lugs on the 100 amp breaker are probably not rated for the two conductors.

 

[Dennis Alwon]

Where are you getting a 70 amp panel? Or are you using a 100 amp panel with a 70 amp breaker?

 

[joshgarcia]

its 70 A rated panel... lug in. Two spaces for branch circuit breakers.

 

[Dennis Alwon]

its 70 A rated panel... lug in. Two spaces for branch circuit breakers.

Gotcha-- now can you feed a 70 amp loadcenter with a 100 amp breaker without a main in the panel? 408.36

 

[fireryan]

Gotcha-- now can you feed a 70 amp loadcenter with a 100 amp breaker without a main in the panel? 408.36

I just read the exceptions in 408.36. If this panel was on a seperate structure would it require the main breaker

 

[kwired]

Put in a double pole breaker to feed the receptacles. Now you have a feeder tap and a MWBC.

 

[joshgarcia]

I thought about putting a double pole breaker before the subpanel, but I was thinking that this fell under the tap rule.

 

[joshgarcia]

I am going to research "tap rule" now, just wanted to throw it out there.

 

[Dennis Alwon]

I thought about putting a double pole breaker before the subpanel, but I was thinking that this fell under the tap rule.

Tap rules depend on the length etc. look at 240.21 for taps

 

[joshgarcia]

If this is an outdoor installation then there is no length limit on tap rule...correct?

 

[Dennis Alwon]

Are you talking about tapping the service entrance conductors before the disconnect? If so then you are correct as there is no overcurrent required until you enter the building.

 

[fireryan]

Are you talking about tapping the service entrance conductors before the disconnect? If so then you are correct as there is no overcurrent required until you enter the building.

How would this differ if you were tapping the feeders instead of the SE conductors

 

[kwired]

Tap rules depend on the length etc. look at 240.21 for taps

If this is an outdoor installation then there is no length limit on tap rule...correct?

Are you talking about tapping the service entrance conductors before the disconnect? If so then you are correct as there is no overcurrent required until you enter the building.

My understanding the entire installation in question is outdoors. No limit on tap length or size as long as it terminates at an overcurrent device and is large enough to carry the load.

If it is tapped from service conductors then it is a service disconnect and not a feeder tap. Better not be more than 5 other disconnects on same structure (the pole in this case) or you will need to do it differently.

 

[Dennis Alwon]

How would this differ if you were tapping the feeders instead of the SE conductors

Tapping the feeders must follow 240.21 but when you tap the service conductors the taps are still service conductors. Service conductors outside follow rules of art. 230.6, 230.70, etc

 

[fireryan]

Tapping the feeders must follow 240.21 but when you tap the service conductors the taps are still service conductors. Service conductors outside follow rules of art. 230.6, 230.70, etc

So the advantage would be you could run a 3wire instead of a 4wire to the service disconnect

 

[kwired]

So the advantage would be you could run a 3wire instead of a 4wire to the service disconnect

That is one difference. It does need a grounding electrode system, where a feeder tap would not except where it serves a separate building or structure.

A feeder tap must terminate at a single overcurrent device. It must not be of less ampacity than the device - some exceptions like motor loads.

A service conductor can supply multiple service disconnecting means - you are usually limited to 6 devices at a particular service location. The service conductor that feeds multiple disconnects usually only needs sized for the calculated load and not necessarily for the total rating of the overcurrent devices.

 

[joshgarcia]

my understanding is that if it is outdoors then there is no limit on length...correct?

 

[kwired]

my understanding is that if it is outdoors then there is no limit on length...correct?

Correct, with conditions.

2008 NEC

240.21...

(5) Outside Taps of Unlimited Length. Where the conductors are located outdoors of a building or structure, except at the point of load termination, and comply with all of the following conditions:
(1) The conductors are protected from physical damage in an approved manner.
(2) The conductors terminate at a single circuit breaker or a single set of fuses that limit the load to the ampacity of the conductors. This single overcurrent device shall be permitted to supply any number of additional overcurrent devices on its load side.
(3) The overcurrent device for the conductors is an integral part of a disconnecting means or shall be located immediately adjacent thereto.
(4) The disconnecting means for the conductors is installed at a readily accessible location complying with one of the following:
a. Outside of a building or structure
b. Inside, nearest the point of entrance of the conductors
c. Where installed in accordance with 230.6, nearest the point of entrance of the conductors

 

[joshgarcia]

if the tap is outdoors then there is no limit on length... correct?