Plans examiner

[Dave Sprague]

We have an electrical engineer that is bidding on the design for an apartment complex. He is proposing a 120/208, 4-wire, 3-phase electrical service to each building. He wants to take advantage of the reductions displayed in Table 310.15A(B)(7) for the feeders to each apartment panel. What he is proposing is clearly outside the parameters of the table and corresponding article. Is there a reason for this limitation?

 

[jumper]

IIRC, the data collected for the creation of the table was done by POCOs. They did not collect data for 120/208, only 120/240 so we cannot use the table for this application.

 

[kingpb]

We have an electrical engineer that is bidding on the design for an apartment complex. He is proposing a 120/208, 4-wire, 3-phase electrical service to each building. He wants to take advantage of the reductions displayed in Table 310.15A(B)(7) for the feeders to each apartment panel. What he is proposing is clearly outside the parameters of the table and corresponding article. Is there a reason for this limitation?

I would be concerned with the fact that a 120/208 V system is not a 3ph, 4wire system. It is a single phase open-wye service using 2 legs off of a 208Y/120V (3ph, 4wire) system.

 

[infinity]

I would be concerned with the fact that a 120/208 V system is not a 3ph, 4wire system. It is a single phase open-wye service using 2 legs off of a 208Y/120V (3ph, 4wire) system.

Although he may have written that incorrectly you're assuming that this is an open-wye service correct?

 

[jdcpe17]

obviously it is not a 120/208 open wye if it is a 3ph/4wire system, so it was probablly a mistake and he meant 208Y/120 system. i think youre assumption of open wye would be wrong here.

i would be somewhat concerned about many appliances running on 208V instead of their marked 240V (what is typical for residential)... reduced life possible.

 

[kingpb]

Although he may have written that incorrectly you're assuming that this is an open-wye service correct?

Did they write 120/208 incorrectly, or did they assume that when the utility told them 120/208 was available, it was assumed it was a 3 ph, 4 wire?

You tell me what the designer assumed, and I'll say what I assumed!

 

[texie]

We have an electrical engineer that is bidding on the design for an apartment complex. He is proposing a 120/208, 4-wire, 3-phase electrical service to each building. He wants to take advantage of the reductions displayed in Table 310.15A(B)(7) for the feeders to each apartment panel. What he is proposing is clearly outside the parameters of the table and corresponding article. Is there a reason for this limitation?

I always felt that 310.15(B)7 was developed based on ONLY 120/240 SINGLE PHASE supply as the neutral current doesn't cancel on single phase feeders fed from a 120/208 3 phase supply and as such there would be more heating of the conductors. This seems similar to the old question of using 310.15(B)7 to fed sub panels and OMO this clearly is not compliant but is done all the time. Some AHJ's even officially sanction it. As a side question, is this by chance related to this post started yesterday? http://forums.mikeholt.com/showthread.php?t=142426

 

[George Stolz]

Dave, welcome to the forum.

The CMP has repeatedly rejected proposals to include 120/208 in 310.15(B)(7), because the original data submitted at it's inception was based on utility data on single-phase 120/240 systems, and due to a concern over neutral loads. Those are their stated reasons for maintaining the 120/240 restriction.

 

[jim dungar]

i would be somewhat concerned about many appliances running on 208V instead of their marked 240V (what is typical for residential)... reduced life possible.

120/208V 1Ph 3W is a very common supply to individual units in housing complexes. Much, if not most, residential equipment is rated for 208-240V supplies for this reason.

 

[texie]

120/208V 1Ph 3W is a very common supply to individual units in housing complexes. Much, if not most, residential equipment is rated for 208-240V supplies for this reason.

Yes, very true. We used to get a lot of complaints from part time residents that had a single family home "up north" (120/240) and then come down to their condo on the beach and find the oven, stove, etc just didn't seem to be working like their stuff up north (in many cases identical models). In rare cases some models actually offered 208 elements as an option.