MI Cable

[Alwayslearningelec]

When determining current carrying capacity of MI which column is used(75 or 90) and whihc table? Thanks.

 

[Alwayslearningelec]

The feeder tag for this MI is 3#6's. Isn't that under sized based on breaker size?

 

[infinity]

I've heard that some engineers size single MI cables using 310.17 for free air. #6@75°C=95 amps

 

[Alwayslearningelec]

Oh..ok so if that's code compliant then it's fine....was hoping it wasn't.

Does it matter if it's 3 conduits under one jacket?

 

[ramsy]

Does it matter if it's 3 conduits under one jacket?

One KO complies with 300.20

Separate KO requires non-ferrous enclosures.

 

[samhutch]

Per 332.80(b), single type mi cables grouped together in a trianglular or square configuration should not exceed ampacities allowed by table 310.17

 

[Alwayslearningelec]

The cables above are run from a 90A breaker to a 90A breaker 350'. According to my VD calculator #6's won't work to keep VD under 3%. Would need #3's. 480v switchboard.

Does that make sense?

 

[infinity]

The cables above are run from a 90A breaker to a 90A breaker 350'. According to my VD calculator #6's won't work to keep VD under 3%. Would need #3's. 480v switchboard.

Does that make sense?

How do you know what the load is for the calculation?

 

[Alwayslearningelec]

How do you know what the load is for the calculation?

I don't know the actual calculated load but it could not be over the 90A, correct?

This is what it feeds....showing panel schedule as well.

 

[infinity]

I don't know the actual calculated load but it could not be over the 90A, correct?

If the load is more than 20 amps I would be surprised.

 

[Alwayslearningelec]

I agree but also have to consider future...there are a lot of spares.

 

[Alwayslearningelec]

Is my post #7 correct?

 

[infinity]

Is my post #7 correct?

My calculator said #2 for 3%VD at 90 amps and 350'.

 

[Boingo1972]

 

[infinity]

View attachment 2582425

That's correct #2. My fat fingers punched in the wrong number on my phone app.

 

[mauk]

You are pretty limited on what loads can be served from the emergency branch. I'd be surprised if future loading ever approached the transformer rating, let alone 90A.