I have seen many designs using ARMS with the instantaneous function applied to the main overcurrent protection device which is in the same enclosure.

But the incident energy is only reduced at the bus side, not in the line side of this device.

The label for that equipment should be the line side incident energy which will be the worst case, unless the equipment manufacturer has certified proper segregation between the line side and the adjacent sections, see IEEE 1584.1.

Therefore, the extra expense dedicate to the maintenance switch is wasted.

Any opinions?

You are correct. The AMS does not affect the device it is 'controlling'.
However it likely reduces the AF incident energy at the equipment downstream from the AMS.

The maintenance switch setting is for the equipment the breaker is feeding. For example, the breaker may feed control panels for equipment and may contain PLCs in it. There are times when the PLC's need to accessed and the arc flash hazard may be high but utilizing the ARMS along with other means, will reduce the arc flash hazard while work is going on it the cabinet

I agree that the ARMS is a good option to reduce the AFIE to equipment that is downstream from it and in a different (separate enclosure).

But installing ARMS that activate the INST function on the main breaker of the panel (which is in the same enclosure of the panel you are interested in mitigate the AFIE) is not a reasonable application.

True. I missed the part about the same enclosure.

I believe the ARMS is not a viable solution for arc flash mitigation as it does not reduce the arc flash energy on the line side of the device it is controlling.

Really??? So if you have a circuit breaker say 100' away from a control cabinet or other piece of equipment that might need troubleshooting or work on while energized and it has an ARMS on it that reduces the IE from say 25 cal/cm2 to 2 cal/cm2, that is not a viable solution for personnel safety?

yes indeed when both the ARMS and the device it is controlling are located within the same enclosure.

I did not understand your comment.

Are you saying that the ARMS works when the main CB (operated by the ARMS) is located in the same enclosure?

If so, I believe you are wrong. The ARMS works when the breaker affected by the switch is located in a separate upstream enclosure.

If you thing differently, I would like to know why.

Thanks.

Maintenance switches trigger an input to the protective relay of the breaker associated with that relay. The zone of protection is everything downstream of that breaker. If you have a main breaker and the ARMS switch triggers the secondary protection settings in THAT breaker - the feeders downstream are protected, but not the main itself.

To lower the IE of the main breaker, the settings of the upstream device must be altered to lower the clearing time of that device.

The ARMS switch can be used in that application if you have a protective device on the upstream breaker and it can accept an input that will put the relay into the secondary settings mode.

Most microprocessor relays can achieve this.

Equipment with main circuit breaker/fuses and MCCs with main circuit breakers I double label the equipment. One label for the line side of the main and the second label for the load side of the main. Them I use black and yellow stripped tape to mark off the boundary of the main circuit breaker. This technique would also apply to a circuit breaker with an ARMS. ARMS are not meant to reduce the line side of the circuit breaker, only the load side.

I will use the ARMS in the main breaker on if the main breaker is completely isolated (like switchgear). I will not use it if there is a possibility of propagation. Ideally I would use the upstream equipment as the main/ARMS.

When we say different enclosure; Are we referring to a segmented MCC with a main ? Our company is currently looking into reduced AFIE for segmented equipment. We are also looking at ARM for other upstream breakers. I understand upstream and downstream protection. I need to read or find clarification and I think this may step into the cascading subject. If anyone has clarification for this please share.

@downriverbill

"When we say different enclosure; Are we referring to a segmented MCC with a main ?"

An MCC with a main that is "segmented" - I believe you are referring to isolation compartments (walls between compartments).

If the MCC is not arc flash rated type, then the isolation walls between compartments will not protect an operator from an arc flash in the MAIN.

The flash will propagate outward taking with it the walls of the gear, doors, etc..

Only arc resistant switchgear is designed to maintain structural integrity under arc fault conditions, and control the pressure and gasses that are created.

Not all arc resistance switchgears are tested to isolate the arc flash in the main section or compartment. Only arc rated switchgear with an additional and optional test does (AR SWGR with the additional Suffix C rating).