Service Upgrade

[KRG9729]

A customer is adding air conditioning to a greenhouse. They are installing 7 - 20 ton units, 7 - 30 ton units, 2 - 5 HP motors, 2 - 7.5 HP motors and 80 single phase blower units. The equipment is all coming from overseas and is rated at 220 volts, 60 hz. The existing service is a 1200 amp, 120/208 3-phase. They had a peak demand last summer of 84KW or 292 amps. The utility company said the transformer can handle up to 2000 amps. To come up with the calculated load I added up all name plate ratings as I was told the system would have a delayed start but will be running at the same time. The total new load I came up with is 449 KW or 1476 amps which I then added for start-up current to bring up the total additional service to 1600 amps. Is this the correct way of calculating or am I missing something? Thank you

 

[Npstewart]

Did you verify the 220v motors can run on 208?

 

[bob]

The existing service is a 1200 amp, 120/208 3-phase. They had a peak demand last summer of 84KW or 292 amps. This appears to be correct if you used a 0.80 power factor. The total new load I came up with is 449 KW or 1476 amps. If you used the name plate information this figure is KVA and no need for a Power factor. 449 KVA = 1248 amps. No need to add start up amps. which I then added for start-up current to bring up the total additional service to 1600 amps. Is this the correct way of calculating or am I missing something? Thank you

.
Your load still appears to exceed the main ampacity. Are you planning to increase it or add another main?

 

[texie]

A customer is adding air conditioning to a greenhouse. They are installing 7 - 20 ton units, 7 - 30 ton units, 2 - 5 HP motors, 2 - 7.5 HP motors and 80 single phase blower units. The equipment is all coming from overseas and is rated at 220 volts, 60 hz. The existing service is a 1200 amp, 120/208 3-phase. They had a peak demand last summer of 84KW or 292 amps. The utility company said the transformer can handle up to 2000 amps. To come up with the calculated load I added up all name plate ratings as I was told the system would have a delayed start but will be running at the same time. The total new load I came up with is 449 KW or 1476 amps which I then added for start-up current to bring up the total additional service to 1600 amps. Is this the correct way of calculating or am I missing something? Thank you

We need to know if the equipment is 3 phase or single phase to make any calculations. Also this load would be considered continuous, so any decision would have to be X1.25. Are the name plate ratings RLA or MCA? This is a fairly large load, so mistakes can be costly.

 

[KRG9729]

Thank you for your replies and I apologize for not getting back early as we had to verify something’s with the customer. I was told they will run on 208 volts but we will have them sign a waiver acknowledging this.

From the beginning:
Existing service: 1200 amp, 120/208, 3?.
Peak demand from last year’s utility bill: 84KW (233 amps)
Existing service also has a 300KW automatic generator before the main switch

Proposed new loads:
Qty. (All Equipment is 3?)
8 30-Ton units Rating per unit = Unit at 220 volts draws 99 amps. I calculated the amperage at 208 by first finding the KW (99 x 220 x 1.732 = 37722.96KW / (208 x 1.732) 360 = 105 x 1.25 (continuous load) = 131.25 amp
6 20-Ton units Rating per unit = 66 amps @ 220 v. Same calculation as above to find amperage at 208 came to 87.5 per unit.
2 7.5 HP pump Rating per unit = 24.2 amps @ 208 volts x 1.25 (continuous load) = 30.25
2 5 HP pump Rating per unit = 16.7 amps @ 208 volts x 1.25 (continuous load) = 20.875

There will also be approx. 40 amps of single phase blower load.

The customer would like to utilize the existing service to power; 2 – 30 ton units and 2- 20 ton units for the generator backup. They would also like to power the pumps and blower which are fed from a PLC panel.
I calculated the load for the existing service as follows:
2- 30 ton units =262.5 amps
2- 20 ton units =175 amps
2- 7.5 HP pumps = 60.5
2- 5 HP pumps = 33.4
40 amps for blowers
Total amperage = 571.4

Proposed New Service
6- 30 ton units = 787.5 amps
4- 20 ton units = 350 amps
Total amperage = 1137.5
1600 amp service

I would appreciate any feedback on this. Also, I have a question on not exceeding 80% of the OCPD. Would I apply the rule per equipment after the 125% was added? For example the 30 Ton unit is rated at 131.25 amps; using the 80% rule I would need a 170 amp breaker? Thank you.

 

[bob]

Thank you for your replies and I apologize for not getting back early as we had to verify something?s with the customer. I was told they will run on 208 volts but we will have them sign a waiver acknowledging this.

From the beginning:
Existing service: 1200 amp, 120/208, 3?.
Peak demand from last year?s utility bill: 84KW (233 amps)
Existing service also has a 300KW automatic generator before the main switch

Proposed new loads:
Qty. (All Equipment is 3?)
8 30-Ton units Rating per unit = Unit at 220 volts draws 99 amps. I calculated the amperage at 208 by first finding the KW (99 x 220 x 1.732 = 37722.96KW / (208 x 1.732) 360 = 105 x 1.25 (continuous load) = 131.25 amp
99 x 1.25 = 124 a
6 20-Ton units Rating per unit = 66 amps @ 220 v. Same calculation as above to find amperage at 208 came to 87.5 per unit.
66 x 1.25 = 83 a
2 7.5 HP pump Rating per unit = 24.2 amps @ 208 volts x 1.25 (continuous load) = 30.25
24.2 x 1.25 = 30.25
2 5 HP pump Rating per unit = 16.7 amps @ 208 volts x 1.25 (continuous load) = 20.875
16.7 x 1.25 = 21 a

There will also be approx. 40 amps of single phase blower load.

The customer would like to utilize the existing service to power; 2 ? 30 ton units and 2- 20 ton units for the generator backup. They would also like to power the pumps and blower which are fed from a PLC panel.
I calculated the load for the existing service as follows:
2- 30 ton units =262.5 amps 248 a
2- 20 ton units =175 amps 166 a
2- 7.5 HP pumps = 60.5 60.5
2- 5 HP pumps = 33.4 42 a
40 amps for blowers
Total amperage = 571.4 557 a

Proposed New Service
6- 30 ton units = 787.5 amps 744 a
4- 20 ton units = 350 amps 332 a
Total amperage = 1137.5 1076 a
1600 amp service


I would appreciate any feedback on this. Also, I have a question on not exceeding 80% of the OCPD. Would I apply the rule per equipment after the 125% was added? For example the 30 Ton unit is rated at 131.25 amps; using the 80% rule I would need a 170 amp breaker? Thank you.

The equipment should have a name plate that gives the max breaker and the min ckt ampacity. For ref equipment the max breaker is 175% of the FLA so for the 30T unit the breaker would be 1.75 x 99 amps = 175 amp breaker. Conductor = 1.25 x 99 = 125 amp capacity. You would not apply the 80% and the 125 % together. Use either one.

 

[KRG9729]

Would a 1200 amp service then be sufficient?

As far as the service goes; we are proposing to install a 1200 amp secondary to a 1200 amp (3 x 4 600kcmil) main disconnect then feed; two 600 amp main breaker panels.

We would also a 600 amp panel from the existing service to serve the units and a 150 amp feed to the PLC.

 

[texie]

Just out of curiosity, why are they using DX A/C in a greenhouse? The only type of cooling I've ever seen in a greenhouse is evaporative.

 

[augie47]

My thoughts:
First, I second what npstewart asked. Have you verified the units are compatible with a 208v service ?

Secondly, how are you obtaining your currents ? You state 99 amps for the 30- ton units. Is that MCA from the nameplate or actual running load ? (The MCA would have a multiplier built-in)

 

[KRG9729]

As posted in a previous post they will run on 208. The units are from another country and all nameplates are in another language... Which is part of the problem.