A sealed dry type transformer was installed in a quazite box, tapping the light pole feed and stepping it down to 120v for receptacles on the poles. (There are several in the lot). The transformers are failing in less than a year and a half. The neutral is bonded at each one to the case. Is this bonding required? A mechanical ground has been run through the system.
general purpose transformer bond
- Thread starter dhuffman
- Start date
- Status
- Location
- Massachusetts
Re: general purpose transformer bond
Yes the bonding is required.
The only way that the bonding could be causing trouble is if there are other problems.
Also do you have proper overcurrent protection?
Grounding electrode?
Yes the bonding is required.
The only way that the bonding could be causing trouble is if there are other problems.
Also do you have proper overcurrent protection?
Grounding electrode?
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: general purpose transformer bond
Typically sealed transformers are not "watertight". Do you have a moisture problem, and don't forget about condensation?
What is your failure mode, such as shorted secondary or open primary?
Typically sealed transformers are not "watertight". Do you have a moisture problem, and don't forget about condensation?
What is your failure mode, such as shorted secondary or open primary?
Re: general purpose transformer bond
Yes, there is moisture present, as they are inside a quazite box. Failure is that the primary fuses blow as soon as they are energized. Overcurrent protection is correct. They are 480v 1ph, 2kva, fused at 4amp on the primary. There is no load, yet the fuses will not hold.
Yes, there is moisture present, as they are inside a quazite box. Failure is that the primary fuses blow as soon as they are energized. Overcurrent protection is correct. They are 480v 1ph, 2kva, fused at 4amp on the primary. There is no load, yet the fuses will not hold.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Re: general purpose transformer bond
How do you know the transformers are bad? I believe your fuses are too small. Often times the highest inrush on a small transformer (i.e. control power) is when it is energized no-load.
A single phase 2KVA transformer with a 480V primary would have a continuous current draw of 4.17A. In general for small transformers, many fuse manufacturers recommend sizing the primary fuses starting at 175%, so in your case this would be a 7-1/2A time delay/dual element fuse.
Per the NEC, to use a fuse this large (more than 167% but less than 250%) on the primary would require the transformer to have secondary protection, in your case this could be a 20A fuse or breaker.
edited: generality
[ August 24, 2004, 05:59 PM: Message edited by: jim dungar ]
How do you know the transformers are bad? I believe your fuses are too small. Often times the highest inrush on a small transformer (i.e. control power) is when it is energized no-load.
A single phase 2KVA transformer with a 480V primary would have a continuous current draw of 4.17A. In general for small transformers, many fuse manufacturers recommend sizing the primary fuses starting at 175%, so in your case this would be a 7-1/2A time delay/dual element fuse.
Per the NEC, to use a fuse this large (more than 167% but less than 250%) on the primary would require the transformer to have secondary protection, in your case this could be a 20A fuse or breaker.
edited: generality
[ August 24, 2004, 05:59 PM: Message edited by: jim dungar ]
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