Alwayslearningelec
Senior Member
- Location
- NJ
- Occupation
- Estimator
They are asking for a 100A breaker on primary 277/280v side. Shouldn't it be a 125A breaker?
Breaker Size
- Thread starter Alwayslearningelec
- Start date
- Location
- New Jersey
- Occupation
- Journeyman Electrician
Is there an OCPD on the transformer secondary at the transformer?
- Location
- Illinois
- Occupation
- retired electrician
A friend of mine works in a facility where they use fusible disconnect for the transformer protection and he will always specify a 100A fuse for a 75 kVA transformer with a 480 volt primary. The 100 amp disconnect is cheaper and physically smaller than the 200 amp one that would be needed for 125 amp fuses.
Alwayslearningelec
Senior Member
- Location
- NJ
- Occupation
- Estimator
The xfrmr is feeding a MCB panel 200' away. That's it for the OCPD.
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
Probably value engineering it. 125 amp is a 200 amp frame.
- Location
- Connecticut
- Occupation
- Engineer
That sounds like a violation of 240.21(C)
- Location
- New Jersey
- Occupation
- Journeyman Electrician
That's a problem. The #4 is also too small for the SSBJ.
If we're talking about a VE opportunity... mount the transformer close to the secondary. The 350's will need upsizing for voltage drop as well with it 210ft away. If you can't move it, you'll have to put a fused disconnect on the secondary next to the transformer.
Also, don't need a neutral conductor on your primary side.
Also, don't need a neutral conductor on your primary side.
Alwayslearningelec
Senior Member
- Location
- NJ
- Occupation
- Estimator
Yes, I did notice that about the neutral
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
In some brands...
ggunn
PE (Electrical), NABCEP certified
- Location
- Austin, TX, USA
- Occupation
- Consulting Electrical Engineer - Photovoltaic Systems
Don't most discos go 30A, 60A, 100A, 200A, 400A, 600A, 800A, 1200A, etc.?
xformer
Senior Member
- Location
- Dallas, Tx
- Occupation
- Master Electrician
What if this is located outside? Wouldn't 240.21(C)(4) apply?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Yes these are the break points for fuse barrel sizes.
Fuse sizes are governed by Listing, breaker sizes are more by manufacturer.
Historically commercial/industrial breaker frame sizes were 100, 225, 400, 800 and 1200A. Residential sizes of 60, 100, and 225 were common
These began to change in the 90s as AIC ratings increased, breakers became faster, and electronic trip units became more common. Today 125/150, 250, 600, and 1200 seem to be the new normal. Residential are typically 100, 150, and 250 (400 A are from the commercial world).
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There's nothing to indicate it's outside, but if it is, 240.21(C)(4) only applies if the feeder is outside and then into a building. In that case, you would need a disconnecting means on the outside of the building where the conduits stub in.
- Location
- San Francisco Bay Area, CA, USA
- Occupation
- Electrical Engineer
I was responding to the frame size comment, frame sizes are in molded case circuit breakers. Some manufacturers have a 100A frame, but some are 125A, some are even 150A. Then some are 200A, or 225, or 250. From there is mostly goes to 400, 600, 800, etc.