10 foot tap rule and auto transfer switches

[Mddocstanley]

Hi and thanks for any input on this.

I am quoting a job that will require a tap(s) (less than 10 feet) from a generator feeder to feed 2 separate ATS's.
The generator is a 60kw and the transfer switches will be 100 amp rated and 200 amp rated.
In Art. 240.21 (B) (1) (2) the requirements do not mention any OCPD as I see mentioned in
Art.21 (B) (5) (2) for taps of unlimited length.
The auto transfer switches do not have OCPD for the generator feeder, only the normal power
feeder (according to what the generator tech that I am working with that will supply the Gener**
ATS's. is telling me)
There is very limited room on this job to mount equipment and if I do not need any OCPD for the
100 amp tap (which will be less than 10 feet) I will not use it.

One other question that I had was under the tap rule for unlimited length, is it also acceptable to bring 2 separate feeders off a breaker that is rated or configured to supply 2 conductors per leg as
tap conductors? In other words a 60kw genset with a 300A breaker with double barrel lugs on each phase leg. To use this point to "tap" a 100 amp feeder and separate 200 amp feeder each going to individual main breaker load centers?

Thanks again for input as I have limited experience in using taps.
M

 

[Dennis Alwon]

Taps in art. 240 all require overcurrent protective device at their terminations if they leave their enclosures. Look at 240.21(B)(4)

 

[augie47]

Are your taps outside ? If so see 240.21(B)(5)

 

[Dennis Alwon]

Are your taps outside ? If so see 240.21(B)(5)

Thanks Gus-- That could be used but they also have to terminate in overcurrent protective device.

If these transfer switch are doing the entire home then they should probably be rated as suitable for service entrance and would have an integral overcurrent protective device.

 

[augie47]

Thanks Gus-- That could be used but they also have to terminate in overcurrent protective device.

If these transfer switch are doing the entire home then they should probably be rated as suitable for service entrance and would have an integral overcurrent protective device.

Good point Dennis. I didn't give that a thought. As I recall, a lot of the SUSE ATS units I see don't have generator overcurrent at the ATS. Of course 225.32 is going to require a OCP at the building unless he can meet the Art 701/702 exception (702.11)

 

[Mddocstanley]

All of the equipment is outside, including feeder and taps.
Dennis---The reference you gave was for taps over 25 feet. I am meeting only
the requirements for a 10 foot tap, Art. 240 (B) (1). In this section the only requirements
for termination are in 240 (B) (1). (2) and (3). In both (2) and (3) of the 10 foot tap section
the code makes reference to not extending beyond the "control device" they supply.
There is no mention of a breaker or fuses that limit the current to the rated current of the tap
conductors as it states for taps of unlimited length.
The control device that the less than 10 foot tap will supply is the auto transfer switch.

Augie42---I will use a service entrance rated transfer switch which I believe will satisfy the service disconnect portion of Art. 225.32 Although there is only partial load of the home to be on alternate power.
I understand the need for an OCPD for the feeder from the generator, which it has, but I do not
see where an additional OCPD is required for the less than 10 foot tap.
If there is a need for OCPD on this tap please give reference..
Thanks again,
M

 

[Dennis Alwon]

All of the equipment is outside, including feeder and taps.
Dennis---The reference you gave was for taps over 25 feet. I am meeting only
the requirements for a 10 foot tap, Art. 240 (B) (1). In this section the only requirements
for termination are in 240 (B) (1). (2) and (3). In both (2) and (3) of the 10 foot tap section
the code makes reference to not extending beyond the "control device" they supply.
There is no mention of a breaker or fuses that limit the current to the rated current of the tap
conductors as it states for taps of unlimited length.
The control device that the less than 10 foot tap will supply is the auto transfer switch.

M

What code book do you have? I go back to 2008 and they all have 240.21(B)(4)-- 10' tap rule. It changed a bit in 2011. Look at the next page for (4) and it mentions overcurrent protective device with field wiring

 

[texie]

All of the equipment is outside, including feeder and taps.
Dennis---The reference you gave was for taps over 25 feet. I am meeting only
the requirements for a 10 foot tap, Art. 240 (B) (1). In this section the only requirements
for termination are in 240 (B) (1). (2) and (3). In both (2) and (3) of the 10 foot tap section
the code makes reference to not extending beyond the "control device" they supply.
There is no mention of a breaker or fuses that limit the current to the rated current of the tap
conductors as it states for taps of unlimited length.
The control device that the less than 10 foot tap will supply is the auto transfer switch.

Augie42---I will use a service entrance rated transfer switch which I believe will satisfy the service disconnect portion of Art. 225.32 Although there is only partial load of the home to be on alternate power.
I understand the need for an OCPD for the feeder from the generator, which it has, but I do not
see where an additional OCPD is required for the less than 10 foot tap.
If there is a need for OCPD on this tap please give reference..
Thanks again,
M

Each transfer switch will have to be protected by an OCPD based on the rating of the switch. You can get transfer switches with factory OCPD on the alternate side if you don't want to provide it separately.

 

[augie47]

Augie42---I will use a service entrance rated transfer switch which I believe will satisfy the service disconnect portion of Art. 225.32 Although there is only partial load of the home to be on alternate power.
I understand the need for an OCPD for the feeder from the generator, which it has, but I do not
see where an additional OCPD is required for the less than 10 foot tap.
If there is a need for OCPD on this tap please give reference..
Thanks again,
M

The service disconnecting means in the ATS would not, IMO, satisfy the 225.32 requirement for a disconnecting means at the building on the generator feeder

plus (below)

Each transfer switch will have to be protected by an OCPD based on the rating of the switch. You can get transfer switches with factory OCPD on the alternate side if you don't want to provide it separately.

I agree with texie, you need OCP rated no higher than the transfer switch

plus

To me, without additional OCP at the ATS the tap conductors would "extend beyond they device they supply" as you would be depending on the 300 amp breaker to protect the conductors on the load side of the ATS when switched to generator.

For all three of the above reasons, my call would be terminate in a OCP at the ATS either integral with the ATS or separate.

 

[Mddocstanley]

Dennis, I do have the 2008 NEC handbook from the NFPA site. It has 240.21 B 1 as the "not over 10' " tap rule. ( I actually went several years back and all had B 1 as the 10 ft. tap rule. B 4 is always the 25 ft tap rule.) I did notice after multiple times missing it, that in condition (1)b that it says "Not less than the rating of the device supplied by the tap conductors OR not less than the rating of the overcurrent protective device at the termination of the tap conductors.
This is the only place in this rule that I see any mention of a OCPD on the tap and in this case its an OR condition not an AND condition. The rating of the device is 100 amp and I will have a #3 cu as the tap conductor.

Even though I cannot find anything so far that tells me I must have an OCPD on this tap, I have decided to quote the job with a MLO panel right at the generator (which is @ 15 ft from the service)
well within sight. I will install OCPD protection here for the 2 individual transfer switches at the service. It seems to me as with Augie47 that having no OCPD on the 100 amp tap that will be connected to the feeder run through the home to a MLO loadcenter, that I would just not be ok with this.
I love to hear opinions, but would also like the code reference if known.
Thanks again everyone!!

 

[augie47]

Notice one of the conditions of 240.21(B)(1) would be that the tap conductors do not extend beyond the device the supply. If the taps supply the ATS, 240.21(B)(1)(2) would not allow the taps to extend beyond the ATS to your panel.

 

[GoldDigger]

If the wired from the ATS to the subpanel were made large enough, the tsp would not extend past the ATS, right?

Tapatalk!

 

[hurk27]

I'm wondering if this is a single 320 meter with double lugs feeding two panels or is this two meters ?

If this is a single meter application then why not just use a single 400 amp service rated ATS with double lugs, then feed the two panels it will eliminate much of the problem? if the ATS is outside, you could hit two disconnects just below the ATS, then the taps would be less then 10' or outside which is unlimited.

Read 240.21(B)(5) and pay attention to (4)(b) and (c) if you might have more room inside.