Manual Transfer Switch O.C. Rating

[jraspino]

We intend to install a SERVICE RATED MANUAL XFER SWT to accommodate a trailer mounted 100Kw 480v 3Ph generator, which will be an OPTIONAL STANDBY SYSTEM.

Would the 2008 NEC permit the use of an 800 A xfer switch mounted between the service entrance conductors and the MDP (which is protected by a 400 A Main Brk). The S.E. conductors are rated for 400 A as well.

Since the Generator and Main Service are both protected by the properly sized O.C. device, we are questioning weather the Xfer Switch must have O.C. protection at all, so long as it's components are S.E. rated and of sufficient size to handle the connected load?

 

[Pierre C Belarge]

There are some variables you have not posted, so I will try my best with this answer.

1. The manual transfer switch that is suitable as service equipment does not is not required to have the Overcurrent device located within the enclosure. The Overcurrent protection is required to be adjacent to the Service rated transfer switch. Is the transfer switch adjacent to the MDP?


2. What is the AIC/AIR rating of the service supply? Does the AIC/AIR rating of the Transfer switch match or exceed that rating?

 

[ceb58]

We intend to install a SERVICE RATED MANUAL XFER SWT to accommodate a trailer mounted 100Kw 480v 3Ph generator, which will be an OPTIONAL STANDBY SYSTEM.

Would the 2008 NEC permit the use of an 800 A xfer switch mounted between the service entrance conductors and the MDP (which is protected by a 400 A Main Brk). The S.E. conductors are rated for 400 A as well.

Since the Generator and Main Service are both protected by the properly sized O.C. device, we are questioning weather the Xfer Switch must have O.C. protection at all, so long as it's components are S.E. rated and of sufficient size to handle the connected load?

Your statement that the trans. switch is service rated means to me that it has built in OCP/DISCO.
If this is the case then the 800amp rating would violate 230.90 A.

 

[augie47]

Your statement that the trans. switch is service rated means to me that it has built in OCP/DISCO.
If this is the case then the 800amp rating would violate 230.90 A.

I have seen manual DT non-fuse disconnects which are service rated, however, as Pierre pointed out, they did not have an AIC rating high enough for the proposed service.

The OP does make me ask why one would use an 800 amp switch ona 400 amp service.

 

[Pierre C Belarge]

Don't you just love when an incomplete question is asked, and then there is no return response... it is like renting a movie, watching an hour and twenty minutes of an hour and thirty minute movie...and then "the scratch" makes it so you cannot see the ending.

 

[jrannis]

This question seems to come up all of the time.

"I have a manual transferswitch that is labeled SE reted, is the proper kaic and amperage for the main OCP.
Question:
Can I use it between the meter and the main OCP? If not, why not? Its SE rated??"

 

[ceb58]

Don't you just love when an incomplete question is asked, and then there is no return response... it is like renting a movie, watching an hour and twenty minutes of an hour and thirty minute movie...and then "the scratch" makes it so you cannot see the ending.

I agree with you Pierre, if I post a question then that means I need an answer.If there is more info needed I supply it because, I need an answer.

But in defence of the OP, since it is his 1st post, he may think it will take days to get even one response. Little dose he know how many of us there are lurking around with nothing better to do than learn and help out if possible

 

[jraspino]

Thank’s for the intelligent replies and questions. Here goes my best attempt at answers.

1. Yes, the xfer switch will be mounted directly adjacent to the existing MDP. Both NEMA 3R enclosures on the exterior of a cement block wall.

2. The available inrush current of the transformer bank is unknown at this time; however this is an existing installation on a commercial building in an area with a very vigilant inspection department. The MDP is an Eaton Pow-R-Line C Panelboard. The inspection dept. does not have an issue with AIC of the existing service.

Since the 800 Amp xfer switch is S.E. rated, we have to take the position that Inrush current is not a problem. Working from those assumptions, do you see any provision in the code that would prohibit us from using this 800 amp switch ahead of the MDP?

 

[ceb58]

Thank?s for the intelligent replies and questions. Here goes my best attempt at answers.

1. Yes, the xfer switch will be mounted directly adjacent to the existing MDP. Both NEMA 3R enclosures on the exterior of a cement block wall.

2. The available inrush current of the transformer bank is unknown at this time; however this is an existing installation on a commercial building in an area with a very vigilant inspection department. The MDP is an Eaton Pow-R-Line C Panelboard. The inspection dept. does not have an issue with AIC of the existing service.

Since the 800 Amp xfer switch is S.E. rated, we have to take the position that Inrush current is not a problem. Working from those assumptions, do you see any provision in the code that would prohibit us from using this 800 amp switch ahead of the MDP?

Aside from the AIC rating
As long as there is OCP/DISCO. (400amp) before the transfer switch (445.18) you should be ok. Same with the disco. for gen. set.

 

[benaround]

Working from those assumptions, do you see any provision in the code that would prohibit us from using this 800 amp switch ahead of the MDP?

Yes, 230.82 , equipment allowed ahead of the service disconnecting means, TS is not on

the list.

 

[augie47]

......................an area with a very vigilant inspection department. The MDP is an Eaton Pow-R-Line C Panelboard. The inspection dept. does not have an issue with AIC of the existing service.

Since the 800 Amp xfer switch is S.E. rated, we have to take the position that Inrush current is not a problem. Working from those assumptions, do you see any provision in the code that would prohibit us from using this 800 amp switch ahead of the MDP?

If the inspection dept is as vigilant as you say, your assumption may bite you. The fact that the existing gear is adequate for the AIC may not help you with the transfer switch as that AIC is likely 10k

Yes, 230.82 , equipment allowed ahead of the service disconnecting means, TS is not on

the list.

benaround, I think the "key" is that this switch becomes the service disconnect and not "ahead of".

 

[RUWired]

Yes, 230.82 , equipment allowed ahead of the service disconnecting means, TS is not on

the list.

Frank, would you consider 230.72(B) as a better reason not to allow the manual transfer switch as a service disconnect.

(B) Additional Service Disconnecting Means. The one or more additional service disconnecting means for fire pumps, emergency systems, legally required standby, or optional standby services permitted by 230.2 shall be installed remote from the one to six service disconnecting means for normal service to minimize the possibility of simultaneous interruption of supply.

Rick

 

[benaround]

Gus, Rick,

I jumped the gun on this one, " immediately adjacent thereto ". So, the MTS becomes the

service disconnect and the MDP if it has a main breaker, remains as the overcurrent pro-

tection. No additional changes to the MDP's n/grd will be needed, is this the way you guys

see it ?

ps. Gus, I like the 'Moderator" with your name, nice touch.

 

[RUWired]

what do you guy's think of 230.72(B) and the use of a manual transfer switch as the disconning means. The article is written to prevent interuption of power to a building by seperating the normal service disc. and the optional power supply disconnect. With both service conductors and generator feeder conductor in the same enclosure, 230.72(B) can't be maintained.Any thoughts?
Rick

 

[benaround]

what do you guy's think of 230.72(B) and the use of a manual transfer switch as the disconning means. The article is written to prevent interuption of power to a building by seperating the normal service disc. and the optional power supply disconnect. With both service conductors and generator feeder conductor in the same enclosure, 230.72(B) can't be maintained.Any thoughts?
Rick

Rick, I think your point is a good one, but, 230.72(B) in part says " or optional standby

'services' permitted by 230.2 ". That would rule out a generator type standby as that is

not considered a service. imo