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Tap with MCS panelboard.

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binwork91

Senior Member
Location
new york
Occupation
electrical engineer
I have a project, tap conductor feeds a panelboard with MCS (molded case switch).

Is MCS a overcurrent protective device?

In my opinion, MCS is not a overcurrent protective device, it does not provide overcurrent protection, it only has a fixed instantaneous self-protecting trip element which may open the switch under high fault conditions, therefore, we can not use 10ft tap, 25ft tap rule to feeds a panelboard with MCS.

What is your opinion?
 
electrofelon

electrofelon

Senior Member
Location
Cherry Valley NY, Seattle, WA
binwork91 said:
I have a project, tap conductor feeds a panelboard with MCS (molded case switch).

Is MCS a overcurrent protective device?

In my opinion, MCS is not a overcurrent protective device, it does not provide overcurrent protection, it only has a fixed instantaneous self-protecting trip element which may open the switch under high fault conditions, therefore, we can not use 10ft tap, 25ft tap rule to feeds a panelboard with MCS.

What is your opinion?
Click to expand...
A molded case switch is just a switch. You need an OCPD at the termination of the tap conductors.
 
charlie b

charlie b

Moderator
Staff member
Location
Lockport, IL
Occupation
Semi-Retired Electrical Engineer
Can you use conductors to feed the panelboard that are large enough to be protected by the upstream overcurrent device? In other words, can you make this not be a "tap"?
 
B

binwork91

Senior Member
Location
new york
Occupation
electrical engineer
charlie b said:
Can you use conductors to feed the panelboard that are large enough to be protected by the upstream overcurrent device? In other words, can you make this not be a "tap"?
Click to expand...
It is not my design, supply house provide the cutsheet for me to do the study, so I think change to MCB is easier.

Not sure which one is cheaper, "change 1set 3/0 cu to 1 set 500kcmil cu" vs "change MCS to MCB".
 
petersonra

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
electrofelon said:
A molded case switch is just a switch. You need an OCPD at the termination of the tap conductors.
Click to expand...
It is not just a switch. It also has a magnetic trip, but no thermal trip. And I think the magnetic trip is a lot more than you would want.

I wonder why the supply house quoted such an odd beast. I don't think I have ever seen a mcs as a main for a panelboard
 
B

binwork91

Senior Member
Location
new york
Occupation
electrical engineer
petersonra said:
I wonder why the supply house quoted such an odd beast. I don't think I have ever seen a mcs as a main for a panelboard
Click to expand...
I think supply house follow the equipment schedule, and equipment schedule might have a typo. It shows as MCB panel, but with a note "MCB shall be Molded case switch".
 
J

jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
petersonra said:
It is not just a switch. It also has a magnetic trip, but no thermal trip. And I think the magnetic trip is a lot more than you would want.

I wonder why the supply house quoted such an odd beast. I don't think I have ever seen a mcs as a main for a panelboard
Click to expand...
The magnetic trip setting is often at a self-protection level to provide a higher short circuit rating than a plain switch. I think UL introduced this about 10 or more years ago.

If have seen these used where someone wants a local disconnect, but they do not want the issues with having two OCPD in series.
 
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