ATS Number of Poles & Overlapping Neutrals

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shespuzzling

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I have a question about ATS semantics. In an ATS, I thought the nubmer of poles indicated the number of switching conductors. So if the neutral was unswitched, it would be a 3-pole ATS, just like in circuit breakers. A 4-pole ATS implies a switching neutral, which can be overlapping or not. Based on this definition, I don't see why one would indicate a 3-pole ATS with an "overlapping neutral", because the neutral is ALWAYS overlapping. I have read various white papers and seen submittals that indicate an ATS as 3-pole and, specifically, with an overlapping neutral. Can you have a 3-pole without an overlapping neutral? I don't see how you could and therefore am confused about why it is mentioned at all. It's like saying a 2-pole receptacle with 2 current carrying condcutors....it's already implied in the number of poles.

Any clarification would be appreciated!
 
It seems to me that if on a 3 phase, 4w system you wanted to switch the neutral in a make-before-break method, you would specify a 4 pole ATS with an overlapping neutral.

In the same way, if on a 1 phase, 3w system you wanted to switch the neutral in a make-before-break method, you would specify a 3 pole ATS with an overlapping neutral.
 
shespuzzling said:
I have a question about ATS semantics. In an ATS, I thought the nubmer of poles indicated the number of switching conductors. So if the neutral was unswitched, it would be a 3-pole ATS, just like in circuit breakers. A 4-pole ATS implies a switching neutral, which can be overlapping or not. Based on this definition, I don't see why one would indicate a 3-pole ATS with an "overlapping neutral", because the neutral is ALWAYS overlapping. I have read various white papers and seen submittals that indicate an ATS as 3-pole and, specifically, with an overlapping neutral. Can you have a 3-pole without an overlapping neutral? I don't see how you could and therefore am confused about why it is mentioned at all. It's like saying a 2-pole receptacle with 2 current carrying condcutors....it's already implied in the number of poles.

Any clarification would be appreciated!
Click to expand...

A 3-Pole ATS with an overlapping neutral would be for single phase use and a 4-Pole ATS with an overlapping neutral would be for three phase use.
A 3-Pole three phase ATS switches only phase poles, the neutrals from both sources and the load are solidly connected together and are not switched.
Overlapping neutral describes a switched neutral pole that is designed to make connection before the phase poles make contact and to break the connection after the phase poles break contact.

http://www.cumminspower.com/www/literature/technicalpapers/PT-6006-GroundingAC-2-en.pdf
 
eHunter said:
A 3-Pole ATS with an overlapping neutral would be for single phase use and a 4-Pole ATS with an overlapping neutral would be for three phase use.
A 3-Pole three phase ATS switches only phase poles, the neutrals from both sources and the load are solidly connected together and are not switched.
Overlapping neutral describes a switched neutral pole that is designed to make connection before the phase poles make contact and to break the connection after the phase poles break contact.

http://www.cumminspower.com/www/literature/technicalpapers/PT-6006-GroundingAC-2-en.pdf
Click to expand...

I could not have said it better, and with the same link. :cool:
 
One last comment.
Yes you can have an ATS that does not have an overlapping neutral where the neutral pole follows and makes and breaks the same time as the phase poles.
 
ATSman said:
One last comment.
Yes you can have an ATS that does not have an overlapping neutral where the neutral pole follows and makes and breaks the same time as the phase poles.
Click to expand...
And if there is any small variation in the contact timing, you have momentarily created a super MWBC with no neutral. Whether it hurts anything will depend on just what the load devices included. :)
 
Tried to edit original comment but couldn't.
so here goes:

Couple of comments.
Yes you can have an ATS that does not have an overlapping neutral where the neutral pole follows and makes and breaks the same time as the phase poles.
There is a type of ATS called a closed transition transfer switch. With this type the phase poles actually parallel (connect together) for a short period in a make before break fashion (around 100ms but not greater than 500ms.)
This type is usually used when the loads are microprocessor based or voltage sensitive.
The two sources are closely monitored and the inphase monitor only allows transfer when they are within 5 electrical degrees.
 
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