Over Current Protection

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controlsdude

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I have an application with a remote motor starter in a remote disconnect panel. There are fuses in a Square D QMB panel that will be feeding the remote disconnect. I didn't think I needed fuses in the remote panel since they already exist in the QMB. Does the NEC validate this?
 
The purpose of the fuses in the upstream panel is to protect the conductors from that point to the remote panel. They do not provide protection for anything inside the remote panel. So the question boils down to whether there is anything inside the remote panel that requires overcurrent protection. If, for example, there is a control transformer and a main line contactor, I think they will need overcurrent protection. That is, I believe, the purpose of having fuses in a motor starter.

As to specific NEC requirements, there is just the general rule that everything must be protected against overcurrent in some fashion. That statement appears in 240.3.

Welcome to the forum.
 
controlsdude said:
I have an application with a remote motor starter in a remote disconnect panel. There are fuses in a Square D QMB panel that will be feeding the remote disconnect. I didn't think I needed fuses in the remote panel since they already exist in the QMB. Does the NEC validate this?
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It is possible that your branch circuit protection (your QMB panel fuses) may be sized to protect your remote panel, in which case you would not need the remote fuses.
 
charlie b said:
The purpose of the fuses in the upstream panel is to protect the conductors from that point to the remote panel. They do not provide protection for anything inside the remote panel. So the question boils down to whether there is anything inside the remote panel that requires overcurrent protection. If, for example, there is a control transformer and a main line contactor, I think they will need overcurrent protection. That is, I believe, the purpose of having fuses in a motor starter.

As to specific NEC requirements, there is just the general rule that everything must be protected against overcurrent in some fashion. That statement appears in 240.3.

Welcome to the forum.
Click to expand...
but if everything is connected electrically, they the fuses in the QMB are in series with all devices in the circuit, and I would think that they would be protecting all devices.
 
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