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Discussion Starter · #1 ·
Here we go again

Rooftop AC unit

MCA is 45.2A (manufacturer)
125% of that is 56.5A
Ampacity is 65A (according to 310.16 @ 75°C)
Conductor is 6 AWG
MOCP 70A (manufacturer)

How do I protect this

a) 60A Safety switch with 60A Fuse
b) 60A Safety switch with 70A Fuse
c) 100A Safety Switch with 70A Fuse
 

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Electrical Simpleton
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3,350 Posts
Here we go again

Rooftop AC unit

MCA is 45.2A (manufacturer)
125% of that is 56.5A
Ampacity is 65A (according to 310.16 @ 75°C)
Conductor is 6 AWG
MOCP 70A (manufacturer)

How do I protect this

a) 60A Safety switch with 60A Fuse
b) 60A Safety switch with 70A Fuse
c) 100A Safety Switch with 70A Fuse
8 awg wire... 60 amp non-fused disco... and a 50 amp HACR rated circuit breaker.

Pete
 

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Electrical Simpleton
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3,350 Posts
8 AWG? How can that be?

With a MCA of 45.2A the branch circuit would be loaded above 80% since 8 AWG allows for 50A max at 75°C
Sorry, I failed to pay attention that you are in Canada... perhaps things up North are different...

In the US what I stated would be compliant.

Pete
 

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Electrical Simpleton
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3,350 Posts
I'm not, just using familiar reference

But... I still don't get it

Could someone explain that 8 awg selection
From what I know, the MCA listed by the manufacturer already includes the 125%. Therefore, the MCA ampacity you have given would be acceptable on an 8 awg conductor in a raceway.

Pete
 

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Electric Al
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4,823 Posts
Nope, and they should not fit anyway.
A F A I K That is correct .

There are many different styles of adaptors , but they can only be used to fuse down .

You can , of course employ fuses that are engineered for different applications and varied uses ... eg ; slo-blo , H R C etc.
 

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Electrical Simpleton
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3,350 Posts
Therefore option b) is not possible

Option a) is the big winner?
If it were my money I would just use a 60 amp non-fused disconnect at the RTU and a 60 amp HACR rated CB at the panel. With 8 awg cu wire all the way.

But, if the nameplate calls for "fuse only" protection you will be stuck with them.

Pete
 
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