Main Panel Disconnect Rating

Specifically, what are your branch circuit devices? And how many do you have. And what is the full load amps of each one of the devices that comprise the "branch circuits"? Is it single phase or three phase? What is the voltage? Is your main disconnect switch a breaker or fuses?

Thanks!

Jeff

The mains supply to the branch circuits is 480Vac 3 phase. I have a total of 9 branch circuits.

1. 480Vac 3phase to Sinamics Drive package, MSP set at 40amps

2. 480Vac 3phase to 6kva transformer for a robot rated breaker is 6amp. Secondary is 220Vac 3 phase Breaker rated at 16amp

3. 480Vac 3phase to 6kva transfomer again breaker rated is 6amp. Secondary is 220Vac 2 phase. Two breakers rated at 10amps

4. 480Vac 2phase to 3Kva transfomer breaker rated at 3amp. Secondary is 115Vac single phase tied one side of secondary to ground. The secondary has multiple branches main breaker for secondary is 20Amps

5. 480Vac 3phase to air conditioner MSP set at 2.5amps max limit on MSP is 3.2Amps

6. 480Vac 3phase to Sitop PSU MSP set to 2.2Amps max limit on MSP is 3.2Amps

7. 480Vac 3phase to Sitop PSU, MSP set to 2.2Amps max limit on MSP is 3.2Amps

8. 480Vac 3phase to motor, MSP set to 2Amps Max limt on MSP is 3.2Amps

9. 480Vac 3phase to motor, MSP set to 2Amps Max limit on MSP is 3.2Amps

According to code I can take the max limits of the adjustable breakers (MSP). Therfore total current for all branch circuits is 74amps.

The main breaker is an ABB 80amp Breaker.

Offer to give them a credit for the 80 Amp breaker and tell them that you won't guarantee anything if they derate the main breaker. By the way aurizon, it's not allowable to protect a 25 HP motor with a breaker which will handle 100 HP according to NEC. Even though the breaker can handle it, the conductors are part of what's being protected.

Hello Tonk

I think you sould review the the design of the primary side protection of the transformer. I end up with a primary current of 7,22 A (6000/(480*1.73)) for the 480/220 6kA. According to C22.10-04 26-256 (Canadian Electrical Code, wich should be near the NEC) I would end up with a max breaker rating of 10 A (7.22*1.25 = 9.021 A) but should be at least 8A

Greetings,

Danny

Danny

I forgot to say that the 6amp is a 5SX D-curve rated breaker. I derated to suit the Robot which has a capacity of 4.KVA This 6Amp D-curve compensates for the inrush to the 6Kva supply transformer.

Thanks

Terry

Oh!

Thanks, it seems that I will have to find more information about D-Curve rated breaker.

Danny

Tonk,

If I'm understanding this configuration correctly, your calculations are correct.

I'm assuming that there is a 3 pole, 80 amp, 600 vac "molded case circuit breaker" inside of an enclosure....this is your main disconnecting means or your overcurrent protection for all of the branch circuit breakers. I'm also assuming that each one of your branch circuit breakers are of the "molded case circuit breaker" type as well, 3 pole or two pole, 600 vac, rated for the amount of amps for the proposed load.

With each branch circuit breaker sized correctly for their respective loads, all devices have the protection that they need.

From the load side of the 80 amp breaker to to the line side of each branch circuit breaker, you will want to run a #4 wire for each phase on the breakers, which I'm sure you already have done. Then, from the load side of each branch circuit breaker, you can run the correct size wire that would match the breaker size.

I'm not quite sure why anyone would want to change the design of this panel. Other than installing fuse blocks and fuses as opposed to circuit breakers, I'm not sure how you could save any additional money.

"It is, what it is".........................

Good luck with this project!

Thanks!

Jeff

Jeff

Thanks.

Terry

?? I am not an electrician, but if you install a machine that takes 25 HP, you must have a switch that handles that amount of power. You then need a run of conduit to your electrical source which may well have a bigger cutoff that feeds 10 machines like yours, and thus is a 250 HP cutoff.

Now you can also use a 100 HP cutoff for your machine that uses only 25 HP. It is a waste of $$, but it conforms to the code. Can you conform to the code and size everything based on your machine and it's cutoff switch. If the machine gets replaced with a 50 HP machine, it will need a new larger 50 HP cutoff