Installing Service rated ATS 277480v. The generator requires a 120v circuit and 240v heater circuit. They want to put xfmr close to ATS for tap and then add a small load center for the 2 breakers supplying gfci and heater. If we install a 15kva XFMR outside, What specific rules do we follow for installing the XFMR? Would I follow 240.21 b5? Or 240.21 B1? I would put breaker on primary side of xfmr and put MLO load center on secondary side? What am I missing?
10' tap or not
- Thread starter mannyb
- Start date
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
Conductors on the primary side of the transformer may use 240.21(B), or they may just comply with the basic 240.21 requirement.
Conductors on the secondary side of the transformer need to comply with 240.21(C), not 240.21(B).
Cheers, Wayne
Conductors on the secondary side of the transformer need to comply with 240.21(C), not 240.21(B).
Cheers, Wayne
Please correct me if Im wrong or what can be done different or better.
primary side Install disconnect using 10' tap rule to transformer secondary side install MLO load center secondary side and wire 20a outlet and 240v heater?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
The secondary side panelboard needs to have a main device per article 408.36.
The secondary side conductors need to be protected per 240.21(C).
The transformer primary needs to be protected per 450.3.
The transformer primary conductors need to be protected per 240.21(B).
Appears you are "tapping" the service to supply the transformer.
As jim notes, the transformer would need primary (and secondary) protection per 450.3
Your conductors connected to the service and supplying the transformer primary overcurrent device would actually be service conductors and not subject to the tap rules.
As jim notes, the transformer would need primary (and secondary) protection per 450.3
Your conductors connected to the service and supplying the transformer primary overcurrent device would actually be service conductors and not subject to the tap rules.