NEED SOME HELP. i HAVE AN EXISTING FACILITY THAT IS FED FROM A PAD MOUNT TRANSFORMER UNDERGROUND TO A MAIN DISTRIBUTION PANEL WITH A MCB. THE FACILITY NOW WANTS TO ADD A STANDBY GENERATOR (100KW). THE PLAN IS TO CUT THE SERVICE ENTRANCE CONDUCTORS BETWEEN THE PAD MOUNT AND THE MDP, BRING THE SERVICE ENTRANCE CONDUTOR INTO A TRANSFER SWITCH FOR THE STANDBY GENERATOR. THE QUESTION HAS ARRISED AS TO WHETHER THE TRANSFER SWITCH HAS TO BE SERVICE ENTRANCE RATED?
TRANSFER SWITCH RATING
- Thread starter taes
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petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- engineer
Re: TRANSFER SWITCH RATING
Random musing.
If the transfer switch is changed to be the service point, would not the GEC and main bonding jumper have to be moved there?
I am assuming they are now in the panel with the MCB.
Random musing.
If the transfer switch is changed to be the service point, would not the GEC and main bonding jumper have to be moved there?
I am assuming they are now in the panel with the MCB.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: TRANSFER SWITCH RATING
Please turn off the ALL CAPS feature. It makes the post harder to read, and is considered to be a form of SHOUTING.
I am not at all sure you can do what you suggest. This type of transformer is required to have protection of its secondary conductors, and you can?t take credit for the primary protection. In its present configuration, the secondary conductors are protected by the main breaker in the service panel. But if you interpose an ATS between the transformer ant the service panel, then the secondary conductors from the transformer to the ATS will not have any protection. I don?t think the Tap Rules of 240.21(C) allow the secondary conductors to terminate at an ATS.
Anyone else agree or disagree with this?
Please turn off the ALL CAPS feature. It makes the post harder to read, and is considered to be a form of SHOUTING.
I am not at all sure you can do what you suggest. This type of transformer is required to have protection of its secondary conductors, and you can?t take credit for the primary protection. In its present configuration, the secondary conductors are protected by the main breaker in the service panel. But if you interpose an ATS between the transformer ant the service panel, then the secondary conductors from the transformer to the ATS will not have any protection. I don?t think the Tap Rules of 240.21(C) allow the secondary conductors to terminate at an ATS.
Anyone else agree or disagree with this?
Re: TRANSFER SWITCH RATING
Sorry about the caps.
Petersonra I agree with your last statement.
Charlie B - The discussion in the office is that if you break the service entrance conductors at the ATS, then the ATS becomes Service entrance Rated with a MCB,i.e first means of diconnect. Other argument is that you have placed a device that will only operate for a extended period of time during a complete power outage, and service entrance conductor are continuous unless a power outage.
I don't understand the tap rule, because there is no tapping of conductors, just a make or break situation.
I am of the opion it has to be service entrance rated. Just wanted to see what others though of this situation.
Sorry about the caps.
Petersonra I agree with your last statement.
Charlie B - The discussion in the office is that if you break the service entrance conductors at the ATS, then the ATS becomes Service entrance Rated with a MCB,i.e first means of diconnect. Other argument is that you have placed a device that will only operate for a extended period of time during a complete power outage, and service entrance conductor are continuous unless a power outage.
I don't understand the tap rule, because there is no tapping of conductors, just a make or break situation.
I am of the opion it has to be service entrance rated. Just wanted to see what others though of this situation.
wirenut1980
Senior Member
- Location
- Plainfield, IN
Re: TRANSFER SWITCH RATING
I was also wondering if this was considered a tap? I thought this type of configuration was pretty common (i.e normal utility power and generator to an ATS to a panel)? If not common, what is different about it?
I was also wondering if this was considered a tap? I thought this type of configuration was pretty common (i.e normal utility power and generator to an ATS to a panel)? If not common, what is different about it?
- Location
- Massachusetts
Re: TRANSFER SWITCH RATING
IMO if these are service entrance conductors a transfer switch installed as described would have to become the service disconnect and be service rated.
Take look at 230.82 Equipment Connected to the Supply Side of Service Disconnect.
Transfer switches are not in the list.
That IMO means it must be transfer switch that can also serve as the service disconnect which a "service rated" transfer switch can do. It will have accessible manual disconnect ability.
There is also 230.66 which requires it to be identified suitable for service equipment.
IMO if these are service entrance conductors a transfer switch installed as described would have to become the service disconnect and be service rated.
Take look at 230.82 Equipment Connected to the Supply Side of Service Disconnect.
Transfer switches are not in the list.
That IMO means it must be transfer switch that can also serve as the service disconnect which a "service rated" transfer switch can do. It will have accessible manual disconnect ability.
There is also 230.66 which requires it to be identified suitable for service equipment.
crossman
Senior Member
- Location
- Southeast Texas
Re: TRANSFER SWITCH RATING
I agree with iwire on this one. The ATS will need to be on the load side of the service disconnect most likely.
I agree with iwire on this one. The ATS will need to be on the load side of the service disconnect most likely.
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: TRANSFER SWITCH RATING
The phrase ?Tap Rule? is a conversational (i.e., slang) term. But I know of no other simple word or phrase that conveys this concept. The related code section says that it is permissible, under certain circumstances, not to install an overcurrent protective device at the secondary terminals of the transformer. Going from the transformer to the main panel is one of them. Going from the transformer to an ATS, and from there to the main panel, is not one of them.
I am not sure I understand this sentence. Are you saying that this concept has the conductors from the transformer connecting to a Main Circuit Breaker (MCB), or to a disconnect (i.e., no overcurrent protection)?
- Location
- Lockport, IL
- Occupation
- Semi-Retired Electrical Engineer
Re: TRANSFER SWITCH RATING
To wirenut, iwire, and crossman:
Am I right in believing that a disconnect would not be enough? I agree that the ?service disconnect? would have to be at the ATS. I also agree with Bob Peterson that this would alter the required configuration of GECs and bonding jumpers and EGCs. But would that disconnect not also have to be fused? Otherwise, what provides protection for the secondary conductors from the transformer to the disconnect?
To wirenut, iwire, and crossman:
Am I right in believing that a disconnect would not be enough? I agree that the ?service disconnect? would have to be at the ATS. I also agree with Bob Peterson that this would alter the required configuration of GECs and bonding jumpers and EGCs. But would that disconnect not also have to be fused? Otherwise, what provides protection for the secondary conductors from the transformer to the disconnect?
crossman
Senior Member
- Location
- Southeast Texas
Re: TRANSFER SWITCH RATING
I say it would need to be a fused disconnect listed as use for service equipment ahead of the ATS.
I say it would need to be a fused disconnect listed as use for service equipment ahead of the ATS.
wirenut1980
Senior Member
- Location
- Plainfield, IN
Re: TRANSFER SWITCH RATING
It would be nice if the code had some reference in 240.4(F) or Table 240.4(G) to our situation...
I know I am grasping at straws here, but 705.30(C) Transformers. Overcurrent for a transformer with a source on each side shall be provided in accordance with 450.3 by considering first one side of the transformer, then the other side of the transformer, as the primary.
Could this situation be viewed as a transformer having a power source on both sides? If so, then this would support Charlie's point of view, of which I am in agreement with intuitively if I were designing this.
It would be nice if the code had some reference in 240.4(F) or Table 240.4(G) to our situation...
I know I am grasping at straws here, but 705.30(C) Transformers. Overcurrent for a transformer with a source on each side shall be provided in accordance with 450.3 by considering first one side of the transformer, then the other side of the transformer, as the primary.
Could this situation be viewed as a transformer having a power source on both sides? If so, then this would support Charlie's point of view, of which I am in agreement with intuitively if I were designing this.
- Location
- Massachusetts
Re: TRANSFER SWITCH RATING
IMO being service rated it will contain OCP.
Here is a one that could do the job.
Units from 150 to 4000 amp available in 3R, 4X and 12 enclosures.
Service Entrance Power Transfer Switch
IMO being service rated it will contain OCP.
Here is a one that could do the job.
Units from 150 to 4000 amp available in 3R, 4X and 12 enclosures.
Service Entrance Power Transfer Switch
crossman
Senior Member
- Location
- Southeast Texas
Re: TRANSFER SWITCH RATING
Nice job iwire! That is sweet.
Nice job iwire! That is sweet.
Re: TRANSFER SWITCH RATING
I think I agree with Iwire. The transfer switch has to be service rated to be the service disconnect. And it seems likely that any transfer switch that is service rated will have OCP on the utility side.
Steve
I think I agree with Iwire. The transfer switch has to be service rated to be the service disconnect. And it seems likely that any transfer switch that is service rated will have OCP on the utility side.
Steve
crossman
Senior Member
- Location
- Southeast Texas
Re: TRANSFER SWITCH RATING
2005 Code Section 230.91 Location
"The service overcurrent device shall be an integral part of the service disconnecting means or shall be located immediately adjacent thereto."
So a service rated Xfer switch with no OCP would have to have an additional component in the installation
[ January 14, 2005, 02:45 PM: Message edited by: crossman ]
2005 Code Section 230.91 Location
"The service overcurrent device shall be an integral part of the service disconnecting means or shall be located immediately adjacent thereto."
So a service rated Xfer switch with no OCP would have to have an additional component in the installation
[ January 14, 2005, 02:45 PM: Message edited by: crossman ]
Re: TRANSFER SWITCH RATING
To address the original post I know that there is one breaker type ATS manufaturer who does have a service entrace labeled ATS which would address your problem of landing the service entrance conductors directly on the transfer switch.
Re: TRANSFER SWITCH RATING
Just want to thank everyone for the insight and replies. It has given us alot to discuss and think about.
To clarify some things, this is a utility pad mount transformer, that feeds the MDP at the building. So in this situation the secondary side is from the utility provided transfomer.
In all my reading and research that I can find, a service rate ATS has OCP ahead of the transfer switch. All this is in one enclosure.
Thanks again!
Just want to thank everyone for the insight and replies. It has given us alot to discuss and think about.
To clarify some things, this is a utility pad mount transformer, that feeds the MDP at the building. So in this situation the secondary side is from the utility provided transfomer.
In all my reading and research that I can find, a service rate ATS has OCP ahead of the transfer switch. All this is in one enclosure.
Thanks again!
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