Flex From Xfrm To/From Panel

[Alwayslearningelec]

If you has transformer located about 2-4' from panel it was feeding/being fed from would you run FMC into the panel if the xfmr was(as usual) utilizing FMC or would you transition over to EMT? Not sure if allowed by code.

 

[infinity]

You can use a non flexible raceway (i.e-EMT), a flexible raceway (i.e.- FMC) or a combination of both. At 2-4' I might opt for FMC only. Sometimes the spec limits the length. We've seen limits as short as 18" for the flex.

 

[Alwayslearningelec]

You can use a non flexible raceway (i.e-EMT), a flexible raceway (i.e.- FMC) or a combination of both. At 2-4' I might opt for FMC only. Sometimes the spec limits the length. We've seen limits as short as 18" for the flex.

Yes that is what I was thinking, the distance is so short FMC might make more sense.

 

[infinity]

Is the transformer floor mounted? If so you can go straight in with a non flexible raceway.

 

[Alwayslearningelec]

Is the transformer floor mounted? If so you can go straight in with a non flexible raceway.

It's wall mounted? Why can you go directly into with non flexible metal raceway if floor mounted. I thought all xfrm's has to have flex out/in?

 

[Strathead]

It's wall mounted? Why can you go directly into with non flexible metal raceway if floor mounted. I thought all xfrm's has to have flex out/in?

He might mean underground fed. Otherwise I agree, that good work practice is flex connection always. For the other part, it is generally about specs, and the company's vision on good workmanship. Most specs limit flex to 6'. OTOH, for a transformer 6' would be long and ugly in many people's opinion, but that also depends on how it is run. Generally anything more than 3 feet, I would likely transition to EMT.

 

[jim dungar]

I thought all xfrm's has to have flex out/in?

That is a design consideration.
Most specifications require a flexible connection to minimize vibration noise from a transformer however, there is no NEC requirement for it.

 

[Alwayslearningelec]

He might mean underground fed. Otherwise I agree, that good work practice is flex connection always. For the other part, it is generally about specs, and the company's vision on good workmanship. Most specs limit flex to 6'. OTOH, for a transformer 6' would be long and ugly in many people's opinion, but that also depends on how it is run. Generally anything more than 3 feet, I would likely transition to EMT.

Makes sense, thanks.

 

[don_resqcapt19]

I thought all xfrm's has to have flex out/in?

There is no requirement for flexible raceways for transformers. Some manufacturers recommend it to reduce noise, but do not require it. If you have loosened the frame hold down bolts, as required by the instructions, the use of flex does very little to reduce noise.
I have seen many transformer hard piped, and use of hard pipe on the secondary will remove the requirement to use a supply side bonding jumper of the wire type.