combo disconnect /motor starter

[jim dungar]

Re: combo disconnect /motor starter

Ronald,

OLR contacts are on the "right" side of the coil due to the old automotive Joint Industrial Council (JIC) standards.

This location makes it very easy to:
a) wire several coils to a single overload relay as required in reversing and multi-speed starters
b) protect the OLR contact from the effects of a short in the control circuit (except for the short jumper from the coil, the contact is always buffered by the coil)

I see no violation with the location of the OLR contact as it is not a switch as defined by the NEC. All switches are contacts but not all contacts are switches (think yellow vehicles and school buses). After a quick walk through my house I found other examples of contacts that are found in grounded conductors, a motor capactitor centrifugal switch and my toaster's control lever (the UL toaster plug is not polarized).

 

[ronaldrc]

Re: combo disconnect /motor starter

Jim

Thanks I agree both of those reasons are good reasons to have the overload contacts on the common side.

B. A very good reason because a short circuit to ground wound either weld them together or open them permanently and we don't want either of those to happen and in the common side it wouldn't.

A. I'm not sure about would have to study a little have never thought about it, might be other circuit configurations to get around interlocks and reversible starters.

Bennie 430-73 is stating having the control switch on the grounded side.

Ronald

[ July 14, 2003, 10:48 PM: Message edited by: ronaldrc ]

 

[don_resqcapt19]

Re: combo disconnect /motor starter

There are a number of large companies that do not permit the overload relay to be on the grounded conductor of the control circuit. These companies require that the overload relay contact be between the control power circuit fuse and the #1 control wire. For the most part this is a design issue as long as the wire from the overload relay does not leave the controller enclosure, because as Bennie said, it would be unlikely that a ground fault would occur within the enclosure.

Jim,
I still have my question about switching the grounded conductor. If a relay is not an Article 404 switch, then what code section says that I can't switch only the grounded conductor with a relay to control the load? It is my opinion that Article 404 applies to relays, including the overload relay. This is based only on the scope statement of Article 404 where it says that this article applies to "all switches, switching devices", and the lack of another code section that forbids the switching of the grounded conductor.
Don

 

[bennie]

Re: combo disconnect /motor starter

We all know the grounded conductor is not switched for safety reasons, not for performance reasons.

In a starter, the fact the control circuit remains energized when the the overload switch opens, is not a safety issue.

There will always be an energized conductor with L-1 and L-2 of a 240 or 480 control.

 

[hbendillo]

Re: combo disconnect /motor starter

I am not sure we answered Beardley's question. A combination motor starter or disconnect usually has a solid neutral connection. In other words there is a terminal block whereby the neutrals are solidly connected withtout switching. Beardley, are you saying that there is a fourth pole to switch the neutral or are you asking us what to do with the neutral?