Voltage Drop Techniques on Low Voltage System
Voltage Drop Techniques on Low Voltage System
(OP)
Hi there. I have a 240v, 1200 amp single phase service for a residence. The length of run is about 1000 feet from the utility transformer to the home. The utility has stated they do not have taps on their transformer. Stepping the voltage up to 480v and then back down to 240v is not an option. If I can boost the voltage to 252v that would reduce the amount of copper in the ground to the home. In lieu of installing massive amounts of copper underground to the home I am considering:
1. Using a buck boost transformer to boost voltage 252v (5%)
2. Using a 1:1 transformer with tap setting up to 5%
Any other techniques to compensate for voltage drop? Voltage regulator?
Thanks.
b
1. Using a buck boost transformer to boost voltage 252v (5%)
2. Using a 1:1 transformer with tap setting up to 5%
Any other techniques to compensate for voltage drop? Voltage regulator?
Thanks.
b






RE: Voltage Drop Techniques on Low Voltage System
You're going to have horrid regulation.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Voltage Drop Techniques on Low Voltage System
Under our codes, the maximum allowable voltage drop is measured in percentage, not Volts.
I suspect that the utility is using a pad mount transformer to service your project.
Is it possible to locate your own pad-mount step-up near where the supply crosses your property line?
Another advantage of the transformer option is that you won't need to run a neutral for a further saving of copper.
Bill
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"Why not the best?"
Jimmy Carter
RE: Voltage Drop Techniques on Low Voltage System
RE: Voltage Drop Techniques on Low Voltage System
I totally agree with waross, the best option is a transformer. If you do the cost calculations, it may seem comparable between installation of heavy cables vs a transformer. Who knows, the distribution company may chip in the transformer and transmit at medium voltage up to the property boundary if there is potential for more load growth in the area.
RE: Voltage Drop Techniques on Low Voltage System
200 Amps, 3% drop, 4 x 3/0 cable per line. You may be able to deduct the 240 Volt loads to reduce the neutral size somewhat.
Note: 10,000 feet is based on 100 Amp loading on the neutral. If you calculate 200 Amps on the neutral, or 100% unbalanced loading,
Then you are looking at over 20,000 feet of 3/0 as the voltage drop must now be a percentage of 120 Volts rather than 240 Volts.
Show your customer the price of 10,000 feet or 20,000 feet of 3/0 copper cable. He may change his wants a little when he sees the cost.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Voltage Drop Techniques on Low Voltage System
Keith Cress
kcress - http://www.flaminsystems.com
RE: Voltage Drop Techniques on Low Voltage System
1200 Amps for a residence?
I took that as a typo and worked with 200 Amps. If it is 1200 Amps for 1000 feet, the cost gets really crazy. Book a tropical vacation on the profits from this job.
For 200 Amps at 240 Volts, my table shows 4 x 3/0 per line.
In the worst case, if all the loads are 120 Volt loads, the maximum possible unbalance is 200 Amps. So we have to consider the voltage drop based on 120 Volts. That takes us up to 6 x 3/0 per line.
A couple of things that will help;
Rather than using 1200 or 200 Amps, we should be using the calculated demand as per code. This will probably drop the current 25% or more.
Demand factors may be applied to the minimum ampacity of the neutral.
If this is really a 1200 Amp service and the customer is adamant that there be no transformer, take the money!
Bill
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"Why not the best?"
Jimmy Carter
RE: Voltage Drop Techniques on Low Voltage System
At some point you have to tell the customer "no" can't be done. Just because they want their house to float on air doesn't mean they get that.. Tiz interesting.
Keith Cress
kcress - http://www.flaminsystems.com
RE: Voltage Drop Techniques on Low Voltage System
RE: Voltage Drop Techniques on Low Voltage System
A higher voltage cable to an underground vault and an underground transformer close to the residence. This would keep the service length shorter and greatly reduce the amount of copper needed.
Is this a 1200 Amp service or was that a typo?
At 1200 Amps the vault will almost be mandatory.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Voltage Drop Techniques on Low Voltage System
Keith Cress
kcress - http://www.flaminsystems.com
RE: Voltage Drop Techniques on Low Voltage System