Transformer Secondary (windings and conductors) Protection

[charlie b]

I could not find this in the tap rules. I am reviewing plans that show a step-down transformer feeding an MLO panel that feeds 4 loads. Is this legal? Where would I find the associated 6-throws rule?

 

[david luchini]

I could not find this in the tap rules. I am reviewing plans that show a step-down transformer feeding an MLO panel that feeds 4 loads. Is this legal? Where would I find the associated 6-throws rule?

That wouldn't comply with the requirements of 408.36. (Assuming you have a 4-wire secondary.)

 

[charlie b]

Thanks, David. That helps. It is a 4-wire secondary. What they are showing on one 225 amp MLO panel are four breakers that add up to 360 amps. The other MLO panel is rated 400 amps, and its four breakers add up to 425 amps. So I will cite that as a violation.

But just for the sake of discussion, if a transformer feeds an MLO panel that has four breakers that total less than the rating of the panel, will that be compliant?

 

[david luchini]

Thanks, David. That helps. It is a 4-wire secondary. What they are showing on one 225 amp MLO panel are four breakers that add up to 360 amps. The other MLO panel is rated 400 amps, and its four breakers add up to 425 amps. So I will cite that as a violation.

But just for the sake of discussion, if a transformer feeds an MLO panel that has four breakers that total less than the rating of the panel, will that be compliant?

408.36 requires that the panelboard be protected by AN overcurrent device having a rating not greater than the rating of the panelboard. Multiple breakers, even if the total rating was less than the panelboard rating, do not meet this requirement.

They would need either an MCB panel, or a separate OCPD before the panel.

 

[jap]

408.36 requires that the panelboard be protected by AN overcurrent device having a rating not greater than the rating of the panelboard. Multiple breakers, even if the total rating was less than the panelboard rating, do not meet this requirement.

They would need either an MCB panel, or a separate OCPD before the panel.

That's interesting for sure.

JAP>

 

[jap]

What allows that install on a new service from a utility transformer where the 6 movement rule is used?

JAP>

 

[charlie b]

Now I understand what you were trying to tell me. Thanks again, David.

 

[david luchini]

What allows that install on a new service from a utility transformer where the 6 movement rule is used?

JAP>

As far as I can tell, nothing allows that in the 2020 Code. (Maybe they've moved that exception to somewhere else?)

408.36 ex 1 allowed it in earlier Codes.

 

[jap]

In that case per the 2020 code will all Group Metering setups require a Main in the Terminal boxes ?

We have POCO's around our area that will not allow such a device between their utility transformer and the line side of the meter bases in a group metering setup regardless of the amount of tenant mains.

Jap>

 

[jap]

Or even meterpacks for that matter.

JAP>

 

[texie]

What allows that install on a new service from a utility transformer where the 6 movement rule is used?

JAP>

Under the 2017 and prior this was allowed as as David mentioned. The reason is this is not a "tap" application, the conductors are service conductors and tap rules do not apply.
For the 2020 edition if you have multiple service disconnects they must be in separate enclosures.

 

[jap]

I'll have to read up on the 2020.

We're not that far along in our area.

Seems like a rather substantial change.

JAP>

 

[electrofelon]

Under the 2017 and prior this was allowed as as David mentioned. The reason is this is not a "tap" application, the conductors are service conductors and tap rules do not apply.
For the 2020 edition if you have multiple service disconnects they must be in separate enclosures.

Just note that the language is a little different for meter enclosures and for those it is "separate compartments" not "separate enclosures". As far as 408.36, I don't think a meter pack is a panelboard so that would not apply.

 

[don_resqcapt19]

I'll have to read up on the 2020.

We're not that far along in our area.

Seems like a rather substantial change.

JAP>

It is a huge change.

(B) Two to Six Service Disconnecting Means. Two to six service disconnects shall be permitted for each service permitted by 230.2 or for each set of service-entrance conductors permitted by 230.40, Exception No. 1, 3, 4, o r 5. The two to six service disconnecting means shall be permitted to consist of a combination of any of the following:
(1) Separate enclosures with a main service disconnecting means in each enclosure
(2) Panelboards with a main service disconnecting means in each panelboard enclosure
(3) Switchboard(s) where there is only one service disconnect in each separate vertical section where there are barriers separating each vertical section
(4) Service disconnects in switchgear or metering centers where each disconnect is located in a separate compartment