240.21(b)(1)

[montoya]

I have a question regarding the tap rule for 240.21(B)(1)-(5).

If a UL instrument or meter is installed that is self protected and isolated such that it requires no fusing (per manufacturer's instructions) and is following the tap rule 240.21(B)(1) through (5), I have the following questions:

1. The device draws two amperes maximum. What size wire is required when tapping off a 480 Volt 1000 amp service?

2. Per this section of the national electric code no fusing or supplementary protection is required as long as the instrument wiring meets the section rules. Correct? In other words, the tap wiring will be less than 10 feet and goes directly to the instrument without fusing, and the instrument is mounted inside of the switchgear.

Thank-you for your help.

 

[jim dungar]

I believe you need to provide fusing to meet the NEC. In this case the manufacturer's self-protection is only supplemental.

 

[steve66]

Also, you still have to protect the wires going to this instrument unless these wires are part of the instrument and included in the UL listing. And, I believe all the tap rules require the tap to terminate in a circuit breaker or set of fuses.

The one exception is rule #1 where the conductors don't leave the enclosure where the tap is made. It sounds like you may be talking about a meter or something similar, so that may fit the bill. But even if that is the case, see Don's comment.

 

[montoya]

The wires don't leave the enclosure where the tap is made and are less than 10 feet. It is a voltage transducer, however the wires are supplied by the installer and are not included with the transducer.

In talking with UL about the listing and the application, they did not think any fusing was required. I referenced the 240.21(B) article when discussing it with them.

 

[Dennis Alwon]

The wires don't leave the enclosure where the tap is made and are less than 10 feet. It is a voltage transducer, however the wires are supplied by the installer and are not included with the transducer.

In talking with UL about the listing and the application, they did not think any fusing was required. I referenced the 240.21(B) article when discussing it with them.

Can't you install a small inline 2 amp fuse and I believe you would be good with any size wire that will be protected by the 2 amp fuse.

 

[montoya]

Can't you install a small inline 2 amp fuse and I believe you would be good with any size wire that will be protected by the 2 amp fuse.

Of course we can, but we aren't the ones doing the installs around the country. The transducer is part of a larger inverter system but since it installs separately we want to understand the relevant NEC code requirements. As I mentioned, our review with UL regarding the 240.21(B) tap rule is that additional fusing is not required, though of course it will be recommended.

So do the code experts here agree with us and UL?

 

[jim dungar]

UL's unofficial interpretation of an NEC requirement is no more valid than mine.

Protection of the device does not mean there is protection of the conductors. Has UL tested the meter and wire combination specifically to see if the 'tap' conductor is protected?

Do you plan to require a disconnecting means for this transducer?

Will this device be tapped on the line side of the service disconnect?

 

[montoya]

UL's unofficial interpretation of an NEC requirement is no more valid than mine.

Protection of the device does not mean there is protection of the conductors. Has UL tested the meter and wire combination specifically to see if the 'tap' conductor is protected?

Do you plan to require a disconnecting means for this transducer?

Will this device be tapped on the line side of the service disconnect?

Please take no offense to my mention of UL's interpretation, I fully understand the the AHJ will be the final arbitrator of the NEC.

Having said that, to your other questions:

This particular transducer does not have the power wires included. From the various comments, it would seem that if the power wiring is included with the transducer and evaluated under the UL listing then fusing would not be required.

However, if the wiring is by others, despite the fact that the unit is self protected, the interpretation of the tap rule is that fusing is still required?

I am confused because the 240(B)(1) rule says no fusing is required from the tap to the device supplied by the tap. Is there an assumption that the only device that can be supplied by the tap is a protective device or is there another relevant section of the code that applies?

Thank-you for replies, it has been very helpful.

 

[augie47]

I find your question interesting and valid.
As you state, if the assembly is covered by the UL (or any NRTL) listing, then the NEC is not relevant.
If it is a field install, the wording of 240.21(B)(1) does seem to indicate the wiring can terminate in a device with no requirement that the device be an overcurrent device.
Historically all the switchboards I have seen have had OCP for internal wiring, but, I don't see the requirement if one meets all the specifics in 240.21(B)(1).
Hopefully another member will provide some insight.

 

[jim dungar]

I am not taking any offense.

I know there are several factory wired devices that are connected using what appear to be tap rules (i.e. "main" surge protectors and light fixtures).

I guess my gut reaction was that this transducer would be connected to the line side of the service equipment, as allowed by 230.82, in which case it would need separate protection under 230.94 exception 3.

I agree with you that 240.21(B)(1)(1)(b) allows a tap to any device rather than specifically an overcurrent protective one.

 

[montoya]

Thanks to everyone for their responses!

You have all been very helpful. This is a great resource.