Transfer Relay

[shaw0486]

Hello,
I am working on a project and the engineer has illustrate on the plans for us to use a 4 pole relay with (2) n.o. & (2) n.o. contacts to control a 20 amp 208 volt receptacle via emergency power and normal power. Essential normal power would be landed on the N.O. contacts and the 120 volt coil will cause the contact to change state until power failure thus acting as a tranfer device. Is this legal in your opinion. I have not yet found a relay UL list or deisigned for this installation. Please any information will be greatly appreciated.

 

[templdl]

Hello,
I am working on a project and the engineer has illustrate on the plans for us to use a 4 pole relay with (2) n.o. & (2) n.o. contacts to control a 20 amp 208 volt receptacle via emergency power and normal power. Essential normal power would be landed on the N.O. contacts and the 120 volt coil will cause the contact to change state until power failure thus acting as a tranfer device. Is this legal in your opinion. I have not yet found a relay UL list or deisigned for this installation. Please any information will be greatly appreciated.

They do have transfer switches that use contactors.

Also, have you considered a reversing contactor that is made up of 2 contactors that are electrically and mechanically interlocked? One could be fed from the normal source and the other from the emergency source. Since lighting contactors a basically the same a contactors used for motors you may be able to use 2 lighting contactors supplied as an assembly that is electrically and mechanically interlock.

 

[Smart $]

They do have transfer switches that use contactors.

Also, have you considered a reversing contactor that is made up of 2 contactors that are electrically and mechanically interlocked? One could be fed from the normal source and the other from the emergency source. Since lighting contactors a basically the same a contactors used for motors you may be able to use 2 lighting contactors supplied as an assembly that is electrically and mechanically interlock.

FWIW...

700.5 Transfer Equipment.
(A) General. Transfer equipment, including automatic transfer
switches, shall be automatic, identified for emergency use,
and approved by the authority having jurisdiction. Transfer
equipment shall be designed and installed to prevent the inadvertent
interconnection of normal and emergency sources of
supply in any operation of the transfer equipment. Transfer
equipment and electric power production systems installed to
permit operation in parallel with the normal source shall meet
the requirements of Article 705.

(B) Bypass Isolation Switches. Means shall be permitted
to bypass and isolate the transfer equipment. Where bypass
isolation switches are used, inadvertent parallel operation
shall be avoided.

(C) Automatic Transfer Switches. Automatic transfer
switches shall be electrically operated and mechanically
held. Automatic transfer switches, rated 600 VAC and
below, shall be listed for emergency system use.

(D) Use. Transfer equipment shall supply only emergency
loads.

 

[Smart $]

Hello,
I am working on a project and the engineer has illustrate on the plans for us to use a 4 pole relay with (2) n.o. & (2) n.o. contacts to control a 20 amp 208 volt receptacle via emergency power and normal power. Essential normal power would be landed on the N.O. contacts and the 120 volt coil will cause the contact to change state until power failure thus acting as a tranfer device. Is this legal in your opinion. I have not yet found a relay UL list or deisigned for this installation. Please any information will be greatly appreciated.

Quit looking for a relay that's UL listed for the purpose. Instead, look for a 2-pole 20A automatic emergency transfer switch or variations on similar keywords. FWIW, an ATS with more poles will work too... use just 2 poles, leaving the other(s) unused.

 

[iwire]

It sounds to me like this would be article 702 installation which means any relay could be used.

Seems doubtful a receptacal would be an article 700 load.

 

[Smart $]

It sounds to me like this would be article 702 installation which means any relay could be used.

Seems doubtful a receptacal would be an article 700 load.

Perhaps. Some people say "emergency power" when they really mean "optional standby power" :angel:

 

[iwire]

Some people say "emergency power" when they really mean "optional standby power" :angel:

Exactly what I am thinking the case is here.

 

[hillbilly1]

RV manufactures use the DPDT relays (electrically held) as transferswitches all the time for transfering from shore power to generator. As others have said, depends on what the load actually is classified for.

 

[templdl]

This is the contactor style as available from Eaton. I'm sure you would want to consider ASCO. but it looks like there are a lot of other manufacturers also.