Voltage drop
- Thread starter JdoubleU
- Start date
- Status
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
Well, an 8 volt drop out of 208 is only 4%, so that is within what many would consider acceptable/normal. The NEC does not care.
The fact that half of that drop is on the service side and half is within the building wiring is also common.
But it does tell you that there is a good chance that when all four fans are running the voltage drop within the building may be unchanged but the voltage drop on the service side may double to be 4% (8V) all by itself. That could be considered a sign of under-capacity in the transformer, service drop and service conductors.
I am being pressured to change the taps on our transformer but I don't think it is necessary. We have a 12470/208 volt transformer that feeds a MDP that feeds 3 buildings. When loads are high the voltage drops to 204. This individuals believes that this will reduce the life of all our motors. I don't believe this to be true unless the motors are 230 volt motors and if this is the case would it make since to get the correct motor? To me this is normal and acceptable voltage drop. Has anyone had to correct the taps on a transformer before? I could really use some help on this one.
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- Occupation
- Licensed Electrician
Drop from 208V to 204V is non-issue. Most motors won't care a bit. I'm just a wire pulling grunt so I can't help you with any numbers or formulas that will help you convince the upper brass, but for what it's worth I think you are right.
kwired
Electron manager
- Location
- NE Nebraska
Unless you have some equipment that can not take much input tolerance in which case you need some kind of power conditioning to ensure the input stays within a specific range, the most common practice I generally see is to have no load supply voltage on the high side maybe 5% or so, so that when voltage drops because of load on the source it hopefully doesn't drop much below what is the true nominal voltage and you can still add some voltage drop for the circuit length and still be within acceptable tolerances.
Around here a 208 volt nominal system usually has a no load voltage of about 215 volts. Your 208 volt motors should be able to handle anything between about 190 and 225 with out any problems, but most would rather see it a little high instead of a little low.
Around here a 208 volt nominal system usually has a no load voltage of about 215 volts. Your 208 volt motors should be able to handle anything between about 190 and 225 with out any problems, but most would rather see it a little high instead of a little low.
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