FMC Supporting

[Alwayslearningelec]

I often see FMC from xfrmr to panel unsupported, granted it's only a few feet. What's the distance limitations for supporting FMC? Thanks

 

[rc/retired]

348.30

Ron

 

[Alwayslearningelec]

348.30

Ron

Thank you.

 

[Alwayslearningelec]

So as far as I can see none of these FMC whips are supported. Does this fall under 348.30(a) exception 2?

 

[rc/retired]

So as far as I can see none of these FMC whips are supported. Does this fall under 348.30(a) exception 2?

View attachment 2569225

I would give them a green tag.

Ron

 

[Alwayslearningelec]

I would give them a green tag.

Ron

What do you mean?

 

[rc/retired]

I would approve the installation. I think the exception allows it.

Ron

 

[letgomywago]

I agree with Ron yes it would pass that way but I would expect there to be 1 strap for the support on the panel side then the exception would apply for the transformer side being unsupported for the short distance.

 

[Alwayslearningelec]

I agree with Ron yes it would pass that way but I would expect there to be 1 strap for the support on the panel side then the exception would apply for the transformer side being unsupported for the short distance.

Not sure what you mean by the xfrm side? A panel FEEDS the xfrmr and a panel is being FED by the xfrmr.

 

[Fred B]

I agree with Ron yes it would pass that way but I would expect there to be 1 strap for the support on the panel side then the exception would apply for the transformer side being unsupported for the short distance.

Yes agree too. 334.30 requires "FMC shall be securely fastened in place by an approved means within 300 mm (12 in.) of each box, cabinet, conduit body, or other conduit termination and shall be supported and secured at intervals...." So it should have at least the one strap at panel side per exception:
"Exception No. 2: Where flexibility is necessary after installation, lengths from the last point where the raceway is securely fastened shall not exceed the following:" Indicates that there must be at least the one strap.

Question as always comes up is What if the section of pipe is so short you can't realistically get a support to attach in between? And then what is a realistic distance to say you "Can't"? Seen connections so short that it is literally fitting to fitting with no pipe visible or just barely visible, where do you clamp then, "realistically".
Seen no exceptions in code for that scenario.

Like the lower right picture above, that really short piece of flex between the panel and xfer, just floating at an angle, how would one realistically comply with "within 12 inches"?

 

[Eddie702]

If it can be supported, it should be. One exception to not supporting it is if needs to move. Neither the panel or the xformer are going to move. Like a belt drive motor that needs to be moved to adjust the V belts and there are a few other exceptions. To me it is supposed to be supported within 12" of a box and 4 1/2' between supports after that. So from the 12" support if you go more than 4 1/2 feet you need another support unless it is a fixture whip or your using another exception.

As far as the minimum length needed to be supported if they let you float for 12", out of a panel It would seem to me that anything 12" and under needs no support over 12" does. Why can't it be secured to the transformer with a minerlac or a piece of strut on the transformer with a strut clamp?

348.30 in the 2023

 

[Fred B]

Why can't it be secured to the transformer with a minerlac or a piece of strut on the transformer with a strut clamp?

I wondered that too. Anything about a transformer enclosure that would prohibit attaching to it? I don't know. Doing mostly residential don't get much into the transformers of this type.

 

[infinity]

Anything about a transformer enclosure that would prohibit attaching to it?

Nothing would prohibit it and it helps to keep the angle connector from turning.

 

[jaggedben]

While the examples in the photos aren't egregious, in my opinion the exception does not apply. Moreover, in most of them it would have been easy to add a strap or two. And with the time saved not using hard pipe, hard to justify not doing it. IMO

 

[wwhitney]

While the examples in the photos aren't egregious, in my opinion the exception does not apply.

Do transformers generally have vibration isolators, and if so are they internal to the case (isolating the transformer from the enclosure) or external to the case? If the latter, then arguably "flexibility is necessary after installation" for the vibration isolators to work as intended.

Cheers, Wayne

 

[infinity]

Do transformers generally have vibration isolators, and if so are they internal to the case (isolating the transformer from the enclosure) or external to the case? If the latter, then arguably "flexibility is necessary after installation" for the vibration isolators to work as intended.

Cheers, Wayne

There are some that have isolation built in between the core and case within the transformer. They usually require the installer to back off the nuts on the mounting bolts to allow the core to "float". More often the vibration elimination is done externally with springs or pads under the transformer frame.

 

[tom baker]

FMC is most often used to make connections easier and not where flexibility is required. One common application is a ceiling hung heater with FMC drooping down to heater. at least a strap at the ceiling could be used

 

[kwired]

Nothing would prohibit it and it helps to keep the angle connector from turning.
View attachment 2569245

Why does so many think you need flex here. I would have ran the EMT all the way to the transformer if I were doing the install pictured here. Nothing wrong with entering near the back either if you don't want the extra bend in the raceway Plenty of room for the conductors below the support for the coils, but if entering near the front you could always use a conduit body for the short turn.

As mentioned there is no need for flexibility here. No prohibition for flex either though. Flex does have more support requirements than non flexible raceways generally do.

That said over the years seems to kind of be an unwritten rule that as long as you have less than ~3 feet of flex nobody makes you put any additional support method on it even if flexibility not required.

 

[electrofelon]

In my experience, it is quite common in the industry to do as shown without support, and similarly, to do the same thing with LFMC and disconnects. Both wiring types have that exception for support if flexibility is needed, but I agree with jaggedben I just don't see either of those situations actually needing flexibility and thus don't feel the exception should apply.

 

[wwhitney]

Why does so many think you need flex here. I would have ran the EMT all the way to the transformer if I were doing the install pictured here.

Again, if the enclosure is on external vibration pads/springs, flexibility is required. Hard piping to the enclosure will restrain it from movement and become the predominant conveyor of vibrations.

[I have no direct experience with how much transformers vibrate, but if somebody when to the trouble to use pads/springs, obviously it's a concern.]

Cheers, Wayne