Transfer Switch

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ghostbuster

Senior Member
There is a lot of confusion surrouinding this issue and many switchgear suppliers also add to this confusion because their sales group SIMPLY do not know.Recently we had to have a switch removed and replaced with a service rated switch.Supplier had to foot the bill for all additional power shutdowns/utility crews and labour to replace it.
 

Michael15956

Senior Member
Location
NE Ohio
There is a lot of confusion surrouinding this issue and many switchgear suppliers also add to this confusion because their sales group SIMPLY do not know.Recently we had to have a switch removed and replaced with a service rated switch.Supplier had to foot the bill for all additional power shutdowns/utility crews and labour to replace it.


I'm assuming that a SR Switch was required because the equip. was installed on the load side of the meter and line side of a breaker panel.
 

Michael15956

Senior Member
Location
NE Ohio
The reason I ask the question is because if the only real difference between the transfer switches is a breaker then where would there be a safety hazard if a non-service rated switch is installed ahead of the building's first disconnect, other then it would be a code violation?

Sure would save a significant amount of work, materials and time to be allowed to install a non-service rated switch and keep the building's existing first disconnect. Unless there is a transfer switch that is service rated but not also a disconnect.
 

ActionDave

Chief Moderator
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Location
Durango, CO, 10 h 20 min from the winged horses.
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Licensed Electrician
The reason I ask the question is because if the only real difference between the transfer switches is a breaker then where would there be a safety hazard if a non-service rated switch is installed ahead of the building's first disconnect, other then it would be a code violation?

Sure would save a significant amount of work, materials and time to be allowed to install a non-service rated switch and keep the building's existing first disconnect. Unless there is a transfer switch that is service rated but not also a disconnect.
You can install a transfer switch after the service disconnect. There are transfer switches that don't have over current protection, but you can't have a transfer switch that does not disconnect something.
 

GoldDigger

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Location
Placerville, CA, USA
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There is also potentially a difference in how the device responds to an unfused (for practical purposes) source of power.
All wiring downstream of a main service disconnect will be protected by a breaker which limits fault current on a time current integral and instantaneous trip basis.
The transfer switch contacts on the line side are not similarly protected if the transfer switch is upstream of the main breaker(s) for the service.
I am curious whether this is reflected in the current withstand and current interrupting ratings of service rated and non service rated TS devices.
The transfer switch is not an OCPD and would not be expected to limit current in the even of a fault, but the same condition that caused the fault current to flow may well cause the transfer switch to activate (if the alternate power source is already active).
 

Michael15956

Senior Member
Location
NE Ohio
There is also potentially a difference in how the device responds to an unfused (for practical purposes) source of power.
All wiring downstream of a main service disconnect will be protected by a breaker which limits fault current on a time current integral and instantaneous trip basis.
The transfer switch contacts on the line side are not similarly protected if the transfer switch is upstream of the main breaker(s) for the service.
I am curious whether this is reflected in the current withstand and current interrupting ratings of service rated and non service rated TS devices.
The transfer switch is not an OCPD and would not be expected to limit current in the even of a fault, but the same condition that caused the fault current to flow may well cause the transfer switch to activate (if the alternate power source is already active).

So, if I'm understanding this right a non-service rated switch install ahead of the first disconnection device will not have any protection for the contacts within the switch and can be a safety hazard?

Thanks, makes sense to me.
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
So, if I'm understanding this right a non-service rated switch install ahead of the first disconnection device will not have any protection for the contacts within the switch and can be a safety hazard?

Thanks, makes sense to me.

Yes, absolutely. Service entrance rated ATS's are used when there isn't a circuit breaker or fused disconnect between the utility source and the ATS.

So there would be nothing to protect the ATS contacts.

Also, there would be no way to disconnect power from the ATS to service it without calling the utility and having them make a trip to shut off the power (and another trip to turn it back on.)

That could make the person paying the bill very unhappy.

So its basically a choice - provide a Service entrance ATS, or provide a separate breaker or fused disconnect in front of the ATS for the utility power.
 

Michael15956

Senior Member
Location
NE Ohio
Yes, absolutely. Service entrance rated ATS's are used when there isn't a circuit breaker or fused disconnect between the utility source and the ATS.

So there would be nothing to protect the ATS contacts.

Also, there would be no way to disconnect power from the ATS to service it without calling the utility and having them make a trip to shut off the power (and another trip to turn it back on.)

That could make the person paying the bill very unhappy.

So its basically a choice - provide a Service entrance ATS, or provide a separate breaker or fused disconnect in front of the ATS for the utility power.

Thanks
 
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