RTUs and cable sizing

[hhsting]

I have the following RTU all 480V three phase with following MCA, breaker size protecting it, distance from breaker to RTU:

RTU 1: MCA: 46A, breaker size: 60A, distance: 150 feet

RTU 13: MCA: 48A, breaker size: 60A, distance:100 feet

RTU 14: MCA: 48A, breaker size 60A, distance: 70 feet

RTU 16: MCA: 50A, breaker size: 60A, distance: 80 feet

RTU 24: MCA: 49A, breaker size: 60A, distance : 60 feet

My question is for each of the RTU wire size should it be #6 AWG or #8 AWG? Assuming voltage drop less than 3%.

 

[texie]

Your conductors can be #8 in all of these (assuming all terminations are rated 75 degree which is likely) as the conductors only need ampacity of the MCA not the breaker size.

 

[bristlepad]

Your conductors can be #8 in all of these (assuming all terminations are rated 75 degree which is likely) as the conductors only need ampacity of the MCA not the breaker size.

Actually it’s #6. #8 THHN is only rated for 45A now. You may be using too old of a code book.


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[texie]

Actually it’s #6. #8 THHN is only rated for 45A now. You may be using too old of a code book.


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????

 

[bristlepad]

????

Allowable Ampacities have changed since 2008


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[augie47]

Actually it’s #6. #8 THHN is only rated for 45A now. You may be using too old of a code book.


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Curious, what Code cycle are you quoting. Still 50 amps in '17

 

[bristlepad]

Curious, what Code cycle are you quoting. Still 50 amps in '17

Well maybe it is a Florida thing because we cannot use #8 THHN copper for 50A circuits now. My code book is at the office so I can’t look at it right now, I’ll look tomorrow.


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[Chamuit]

Are you using NM somewhere along the circuit? Are the local jurisdictions adding restrictions?