Why only one feeder to separate buildings?

[marmathsen]

I have a customer who has two separate feeders to a house from a single service in a detached garage.

I know this is a violation per 225.30. What I don't know is why it's a violation.

I want to be clear to my customer (as well as myself) why this issue should be corrected and why it's a code requirement in the first place. I can't come up with a salient reason that this code exists.

Thanks in advance for the help and I look forward to seeing your responses.

I guess for bonus points...Was it ever allowed in the past to have multiple feeders? Aside from other special conditions where it's allowed?

-Rob G

 

[Little Bill]

I have a customer who has two separate feeders to a house from a single service in a detached garage.

I know this is a violation per 225.30. What I don't know is why it's a violation.

I want to be clear to my customer (as well as myself) why this issue should be corrected and why it's a code requirement in the first place. I can't come up with a salient reason that this code exists.

Thanks in advance for the help and I look forward to seeing your responses.

I guess for bonus points...Was it ever allowed in the past to have multiple feeders? Aside from other special conditions where it's allowed?

-Rob G

Are you sure that those are feeders? You are allowed to have two drops off of a single service at a dwelling but that is for separate structures. Case in point.... 400A service - dual lugs in the meter - one set runs to the house and the other to a garage or other building.

Since you said both run to the house I don't really see how this would fit the scenario above though.

I believe the reason for only one set of feeders has to do with safety of having only one disconnect to turn off. If the fire department had to go in somewhere that had two feeders and thought they had the power off by turning off a panel when in fact they only killed part of the power.
Sort of the same reason for grouping disconnects.

 

[augie47]

I would agree with Bill in that the restriction is probably an offshoot from one building--one service. If that rule is valid from a safety standpoint, it stands to reason it should apply to detached structures also.
Off course both are diluted by exceptions

 

[marmathsen]

Are you sure that those are feeders? You are allowed to have two drops off of a single service at a dwelling but that is for separate structures. Case in point.... 400A service - dual lugs in the meter - one set runs to the house and the other to a garage or other building.

Since you said both run to the house I don't really see how this would fit the scenario above though.

For some added clarification:

The service is a 400A 240v single phase. There are 2 separate 200A service disconnects in the garage.

One disconnect is a 200A fused disconnect that simply supplies a feeder to a 200A panel inside the house.

The second is a 200A panel that supplies branch circuits in the garage as well as a 90A feeder to the house.

I believe the reason for only one set of feeders has to do with safety of having only one disconnect to turn off. If the fire department had to go in somewhere that had two feeders and thought they had the power off by turning off a panel when in fact they only killed part of the power.
Sort of the same reason for grouping disconnects.

I would agree with Bill in that the restriction is probably an offshoot from one building--one service. If that rule is valid from a safety standpoint, it stands to reason it should apply to detached structures also.
Off course both are diluted by exceptions

I thought of this too but couldn't see the difference between two disconnects right next to each other in the house -or- two SERVICE disconnects right next to each other in the garage (which is allowed). Don't they both cause the same potential hazard?

Sent from my Pixel XL using Tapatalk

 

[kwired]

For some added clarification:

The service is a 400A 240v single phase. There are 2 separate 200A service disconnects in the garage.

One disconnect is a 200A fused disconnect that simply supplies a feeder to a 200A panel inside the house.

The second is a 200A panel that supplies branch circuits in the garage as well as a 90A feeder to the house.





I thought of this too but couldn't see the difference between two disconnects right next to each other in the house -or- two SERVICE disconnects right next to each other in the garage (which is allowed). Don't they both cause the same potential hazard?

Sent from my Pixel XL using Tapatalk

I agree with you in that is sort of doesn't make sense that you can have two to six sets of service conductor (connected to same source) and land in two to six service disconnecting means (grouped in one location) but at same time can't have two to six feeder sets supplying same building even if the disconnecting means are all grouped in one location. You can have a single feeder that supplies two to six disconnecting means in that same building though.

Only thing I can come up with that sort of makes sense is if you shut off a feeder breaker at the garage marked "house" and didn't realize there was a second feeder to the house you might think everything in the house is dead though it is not.

 

[jap]

I don't think it has anything to do with safety at all.

Shunt trip main breakers are allowed as a means of disconnect to a building.

The shunt trip button is located outside to trip a main inside which in turn disconnects the power, but, there is still power to the line side of the shunt trip main,so,
actually you have not removed power from the inside of the building.

If the fire department squirts water on the Main Electrical Panel, they would in fact be spraying water on an energized piece of equipment.

I don't know that the rules actually state that the disconnecting means must kill all the power inside a structure, only that the structure must have a service disconnecting means.

JAP>

 

[kwired]

I don't think it has anything to do with safety at all.

Shunt trip main breakers are allowed as a means of disconnect to a building.

The shunt trip button is located outside to trip a main inside which in turn disconnects the power, but, there is still power to the line side of the shunt trip main,so,
actually you have not removed power from the inside of the building.

If the fire department squirts water on the Main Electrical Panel, they would in fact be spraying water on an energized piece of equipment.

I don't know that the rules actually state that the disconnecting means must kill all the power inside a structure, only that the structure must have a service disconnecting means.

JAP>

Spraying water onto disconnecting means isn't too much of a electrical hazard. Especially for a fire fighter wearing typical fire fighting PPE. Direct stream into an enclosure with door open and onto live components is a bigger hazard.

 

[jap]

Spraying water onto disconnecting means isn't too much of a electrical hazard. Especially for a fire fighter wearing typical fire fighting PPE. Direct stream into an enclosure with door open and onto live components is a bigger hazard.

It was more just another example of something that may be presumed dead but it's not.

Jap>

 

[jaggedben]

I think the rationale is for first responders to be able to shut off power to a structure without having to spend hours tracing wires, especially since electrical is not their expertise. That's why multiple disconnects on a service or structure are limited to six and required to be grouped (and why a fire pump disconnect is required to be separated).

I would say that if the two feeders come to the house such that their disconnects are grouped, same as two-to-six discos for a single feeder would be, that ought to be allowed, although I don't think it is allowed strictly by letter of code.

 

[LarryFine]

Since it's sort of on topic, I'm proposing a 60a 240v car-charger circuit to a detached garage that already a has a 120v lighting circuit.

Any issues with two circuits supplying a separate building? Must either or both have a disconnect at the point of entry?

 

[kwired]

I think the rationale is for first responders to be able to shut off power to a structure without having to spend hours tracing wires, especially since electrical is not their expertise. That's why multiple disconnects on a service or structure are limited to six and required to be grouped (and why a fire pump disconnect is required to be separated).

I would say that if the two feeders come to the house such that their disconnects are grouped, same as two-to-six discos for a single feeder would be, that ought to be allowed, although I don't think it is allowed strictly by letter of code.

But the rule is consistent for the most part when it comes to first responders - whether the building is service or feeder supplied - general rule is no more then six disconnects and they need grouped together. What OP is questioning is why must we only have one feeder to a separate building - even though it can have multiple disconnecting means at the separate building that are grouped in one location?

Per NEC you can't run two 200 amp feeders to a separate building. You can run an individual 400 amp feeder and put two 200 amp disconnecting means at the separate building though.

As I earlier mentioned the only thing that does make some sense to me is if you turn off a switch in building 1 that is marked building 2, and didn't realize there was a second switch also feeding building 2 you might mistakenly think everything is dead in building 2.

 

[Wire-Smith]

you all don't think 225.30(B)(2) allows this?

 

[zbang]

For some added clarification:
The service is a 400A 240v single phase. There are 2 separate 200A service disconnects in the garage.
One disconnect is a 200A fused disconnect that simply supplies a feeder to a 200A panel inside the house.
The second is a 200A panel that supplies branch circuits in the garage as well as a 90A feeder to the house.

I'm kinda surprised nobody has asked about why there are two feeders at all (so I will).

Why are there two feeders to the house at all? I'd assume they were installed at different times by someone who wasn't paying attention. Are there enough loads to push the house over the 200A feeder?
.

 

[jaggedben]

you all don't think 225.30(B)(2) allows this?

Well, for one thing, it would have had to have been explicitly approved by the AHJ when installed. That's what special permission means. But also, no, I don't think a house typically needs more than a 200A feeder, or if it did, it's not difficult to spec the right equipment to install up to a 400A feeder.

 

[kwired]

you all don't think 225.30(B)(2) allows this?

Yes, but a 200 amp feeder and a 90 amp feeder don't really fall under "sufficiently large to make two or more supplies necessary". Last I knew 90 amp breakers and 200 amp breakers were fairly readily available. When does this exception possibly kick in? Maybe when those feeders are over 2000 amps.

 

[Wire-Smith]

Yes, but a 200 amp feeder and a 90 amp feeder don't really fall under "sufficiently large to make two or more supplies necessary". Last I knew 90 amp breakers and 200 amp breakers were fairly readily available. When does this exception possibly kick in? Maybe when those feeders are over 2000 amps.

wouldn't you consider two smaller feeders a safer installation than a 2000 amp feeder?

 

[kwired]

wouldn't you consider two smaller feeders a safer installation than a 2000 amp feeder?

What is your justification for safer?

If in the future people work on this without wearing proper PPE - maybe two smaller feeders results in lower arc flash incident energy levels. Voltage to ground and potential shock hazards remain the same.

 

[Wire-Smith]

What is your justification for safer?

If in the future people work on this without wearing proper PPE - maybe two smaller feeders results in lower arc flash incident energy levels. Voltage to ground and potential shock hazards remain the same.

-lower ocpd, if a fault would occur it is more likely to be opened at a lower current

-smaller wire so you will likely lower available fault current because of line impedance

-knit picking, but doesn't higher currents produce more induced voltage. usually not a safety issue but it's better without (like i said knit picking)

kind of more of a gut feeling for me, haven't thought about it much, i might be wrong that's why i'm asking other's thoughts

 

[kwired]

-lower ocpd, if a fault would occur it is more likely to be opened at a lower current

-smaller wire so you will likely lower available fault current because of line impedance

-knit picking, but doesn't higher currents produce more induced voltage. usually not a safety issue but it's better without (even if only marginally)

Some of those items may deserve some consideration. Still not going to be too significant of difference in many applications between a 200 amp feeder and a 90 amp feeder.

I think especially on smaller capacity feeders (like at least 1200 amp and less) there is still more safety advantage to knowing you shut off the entire building with that one switch then there is to turn off two or three switches and then find out the hard way that there was another switch that needed to be turned off.

 

[Wire-Smith]

Some of those items may deserve some consideration. Still not going to be too significant of difference in many applications between a 200 amp feeder and a 90 amp feeder.

I think especially on smaller capacity feeders (like at least 1200 amp and less) there is still more safety advantage to knowing you shut off the entire building with that one switch then there is to turn off two or three switches and then find out the hard way that there was another switch that needed to be turned off.

225.32 and 225.33
i would expect the disconnects to be together and labelled clearly

if your turning off an entire building why not just blindly open all the disconnects that are sitting there beside each-other?