check my idea- 480 Volt machine taps

[florida-sparkey]

Hello all,
Two 3 phase 480 Volt machines- (50Amp air compressor and 13Amp air dryer)
I intend to wire 2 machines from a single 100Amp breaker.
I will go from panel about 2 feet into a small wire way (4x4x48" troffer) with #3 AWG CU. I will use Polaris 3 position connectors and splice two taps to each conductor. #10 AWG CU and #6 are the tap sizes.
the taps will be no more than 3 feel long and will terminate in fused discos with 70Amp and 15Amp current limiting fusees (MOCPD per nameplates.)
#8 AWG CU will be used for grounding/ bonding to the disconnects.
Both ground and conductors will be reduced on the load side of the disconnects (sized per breaker / load)
My EMT will be bonded for circuits over 151 Volts.
Thank you for the input!!

 

[augie47]

As far as the tap rules are concerned all looks compliant +.
Depending on the actual size of the motors involved, the type starting (ACL?) and the two loads starting simultaneously the 100 amp breaker might be undersized.

 

[florida-sparkey]

As far as the tap rules are concerned all looks compliant +.
Depending on the actual size of the motors involved, the type starting (ACL?) and the two loads starting simultaneously the 100 amp breaker might be undersized.

Thank you,
This is a repair of a horribly incorrect install. The 100 Amp breaker has been running (and protecting???!:rant the equipment for a long time now.

 

[david luchini]

I will use Polaris 3 position connectors and splice two taps to each conductor. #10 AWG CU and #6 are the tap sizes.
the taps will be no more than 3 feel long and will terminate in fused discos with 70Amp and 15Amp current limiting fusees (MOCPD per nameplates.)
#8 AWG CU will be used for grounding/ bonding to the disconnects.
Both ground and conductors will be reduced on the load side of the disconnects (sized per breaker / load)

#6 tap to a 70A OCPD is not compliant with 240.21(B).

And I don't see how you would be able to reduce the ground conductor on the load side of the 70A Disc. It would remain #8.

 

[augie47]

thanks, david. I'm slipping this morning

 

[florida-sparkey]

#6 tap to a 70A OCPD is not compliant with 240.21(B).

And I don't see how you would be able to reduce the ground conductor on the load side of the 70A Disc. It would remain #8.

Thank you all for you help!!

I apologize for the typos, was in a rush. Yes, #4 CU for the 70 Amp and the ground will remain #8

 

[florida-sparkey]

#6 tap to a 70A OCPD is not compliant with 240.21(B).

And I don't see how you would be able to reduce the ground conductor on the load side of the 70A Disc. It would remain #8.

David,
Well.... in hind sight, I DID MISS the #6 wire to a 70Amp breaker in a TAP part! Was in a rush to design and type and I just looked at the 50 Amp load.
Thank you for the input and correction!!

 

[JRW 70]

Compressor w. Dryer

Compressor w. Dryer

On the compressed air systems that I have
dealt with, there was an interlock forcing the
dryer to come on first. Then the compressor
control relay would permit the compressor
starter to close. This ensured no moisture in
the tanks. The process this setup was for was
extremely intolerant of moisture, however.
So it may be worth checking what this air is
used for, and if dryer start shortly before the
compressor start is needed. ( Either for the
process, or just to reduce combination starting
amperage )

JR

 

[florida-sparkey]

On the compressed air systems that I have
dealt with, there was an interlock forcing the
dryer to come on first. Then the compressor
control relay would permit the compressor
starter to close. This ensured no moisture in
the tanks. The process this setup was for was
extremely intolerant of moisture, however.
So it may be worth checking what this air is
used for, and if dryer start shortly before the
compressor start is needed. ( Either for the
process, or just to reduce combination starting
amperage )

JR

Thank you JRW,
These units have been in place for years. A in house thermal imaging guy found a hot spot on a disco. That got me involved. I found that everything was wrong to include the discos are only rated at 240V. I have no intention of changing the units controls or settings, just need to get safe power to the L1 L2 L3 connections.