Overcurrent Protection Question

[Machiavelli999]

We are replacing an air handler on a high rise building. The existing air handler is fed off of a 208V switchboard with an 800A breaker. However, the wires that were installed have an ampacity of just 500A. I am assuming this is because of motor load rules that allow for the overload in the air handler starter to act as the overcurrent protection.

The new unit we are providing has an MOCP of 450A and the owner was planning on just reusing the existing circuit. Question is can we simply install a 450A fuse ahead of the air handler or must the breaker at the switchboard be replaced?

I had thought the OCPD protects the feeder so I personally did not think the 800A breaker at the switchboard would be acceptable.

 

[petersonra]

We are replacing an air handler on a high rise building. The existing air handler is fed off of a 208V switchboard with an 800A breaker. However, the wires that were installed have an ampacity of just 500A. I am assuming this is because of motor load rules that allow for the overload in the air handler starter to act as the overcurrent protection.

The new unit we are providing has an MOCP of 450A and the owner was planning on just reusing the existing circuit. Question is can we simply install a 450A fuse ahead of the air handler or must the breaker at the switchboard be replaced?

I had thought the OCPD protects the feeder so I personally did not think the 800A breaker at the switchboard would be acceptable.

Does the CB have a dial to change the setting at which it trips? maybe you don't need to add a fuse at all.

240.6 Standard Ampere Ratings.
(C) Restricted Access Adjustable-Trip Circuit Breakers. A
circuit breaker(s) that has restricted access to the adjusting
means shall be permitted to have an ampere rating(s) that is
equal to the adjusted current setting (long-time pickup
setting). Restricted access shall be defined as located behind
one of the following:
(1) Removable and sealable covers over the adjusting means
(2) Bolted equipment enclosure doors
(3) Locked doors accessible only to qualified personnel

A 450 A Cb might be more cost effective than a 600 A fusible switch with fuses.

 

[codequestion]

Does the CB have a dial to change the setting at which it trips? maybe you don't need to add a fuse at all.



A 450 A Cb might be more cost effective than a 600 A fusible switch with fuses.

You say more cost effective. How do you know? Is there a place, book, link etc you guys can look up cost of all electrical items?

Sent from my SM-G935U using Tapatalk

 

[zog]

We are replacing an air handler on a high rise building. The existing air handler is fed off of a 208V switchboard with an 800A breaker. However, the wires that were installed have an ampacity of just 500A. I am assuming this is because of motor load rules that allow for the overload in the air handler starter to act as the overcurrent protection.

The new unit we are providing has an MOCP of 450A and the owner was planning on just reusing the existing circuit. Question is can we simply install a 450A fuse ahead of the air handler or must the breaker at the switchboard be replaced?

I had thought the OCPD protects the feeder so I personally did not think the 800A breaker at the switchboard would be acceptable.

What type breaker and trip unit?

 

[petersonra]

You say more cost effective. How do you know? Is there a place, book, link etc you guys can look up cost of all electrical items?

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I said it might be more cost effective. It depends on a lot of factors including what your company pays for things, which can vary wildly from distributor to distributor and among companies buying from them.

OTOH, shutting down the switchboard to change out a CB might not be real cost effective or conveneint even if the parts cost is less.

 

[jap]

You say more cost effective. How do you know? Is there a place, book, link etc you guys can look up cost of all electrical items?

Sent from my SM-G935U using Tapatalk

A 600 amp 600v Fused 3r disconnect with fuses could easily run 3 grand.


JAP>