Breaker Switching Arrangement Wired Reversed

[nightfox1925]

May I know the technical issues at hand if somebody get's "creative" and wires the line wires to the load side of an MCCB and consequently, wire the load wires to the line side of the MCCB?

 

[dpc]

This is termed reverse feed and will violate the UL listing for the breaker unless it is specifically listed for reverse feed.

A lot of new MCCBs are rated for reverse feed, but certainly not all.

 

[waross]

There are exceptions but in many plants all the breakers are top fed and mounted vertically with the line terminals uppermost.
Bottom feeding may create a safety issue for troubleshooters who expect all breakers to be top fed.
Historically, in the early days of electrification, lighting was controlled by open knife switches. The code required that when knife switches were installed vertically, they must be installed so that gravity would NOT tend to close them. They were also required to be wired so that the knife blade would be dead when the switch was open. As a result of these rules knife switches were always top fed and the blades were dead when the switch was open. These requirements are still in the Canadian Electrical Code. They still apply to many disconnect switches. Although breakers are not covered by these rules, many industries and consultants will only accept top feeding as a plant standard.

Bill
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"Why not the best?"
Jimmy Carter

 

[resqcapt19]

Actually the UL listing says that all listed molded case breakers are suitable for "reverse" feed unless their terminals are marked "line" and "load" by the breaker manufacturer.