• 100% Satisfaction Guarantee
Norm, Master Electrician
Category: Electrical
Satisfied Customers: 67
Experience:  Registered professional electrical engineer and licensed master electrician.
62872871
Norm is online now

# I am installing a 75 KVA 208 3P to 440 3P transformer. What

### Customer Question

I am installing a 75 KVA 208 3P to 440 3P transformer. What gauge wire should I use (in and out of the transformer) and what size breaker into the transformer?
Submitted: 3 years ago.
Category: Electrical
Expert:  Rich replied 3 years ago.

Rich :

Hello .. Rich here .. I can help you with this what is the amperage of the panel you are feeding with this transformer ?

JACUSTOMER-km5f2c19- :

200a

Rich :

For the 200 amp service you would need 2/0 copper or 4/0 aluminum .. out of the transformer

Rich :

the primary of this transformer will draw about double the current 450 amps .. that would take 400 kcmil and a 450 amp breaker

Customer: replied 3 years ago.

Just re-read your question the load on the 440 3p side of the transformer will not exceed 90A...

Expert:  Rich replied 3 years ago.
Yes. And you are wiring it to a. 200amp panel
Expert:  Rich replied 3 years ago.
Using the 75kva xformer you would have 350amps in and 155 amps out. So. Wire the primary with 350 copper to a 350 amp bkr.
Customer: replied 3 years ago.

Each phase? Doesnt seem to add up...what is the math?

208V 3p in

440V 74 KVA load at 89 amps - rating on the equipment

75 KVA transformer

Expert:  Norm replied 3 years ago.

Hi, I'm Norm.

The primary (208 V.) current for the 75 kVA transformer is, coincidentally, 208 Amps. A breaker for that side must be at least 1.25 times that value, or 260 Amps. The next standard overcurrent device is 300 Amps, so use that with 300 kcmil copper wire with THHN insulation, no more than 3 current-carrying conductors in conduit. The secondary (480 V.) current is 90 Amps, so you can use #4 copper with THHN insulation, also no more than three current-carrying conductors in conduit. I use 480 Volts rather than 440 Volts as that is the standard utility voltage today, even though your load may have a 440-Volt nameplate.

Ask-a-doc Web sites: If you've got a quick question, you can try to get an answer from sites that say they have various specialists on hand to give quick answers... Justanswer.com.
...leave nothing to chance.
Traffic on JustAnswer rose 14 percent...and had nearly 400,000 page views in 30 days...inquiries related to stress, high blood pressure, drinking and heart pain jumped 33 percent.
Tory Johnson, GMA Workplace Contributor, discusses work-from-home jobs, such as JustAnswer in which verified Experts answer people’s questions.
I will tell you that...the things you have to go through to be an Expert are quite rigorous.

### What Customers are Saying:

• You did one super job of explaining to me everything there is to know about this fridge. I'm looking forward to asking you questions in the future. Jimmy Bagley, IA
< Previous | Next >
• You did one super job of explaining to me everything there is to know about this fridge. I'm looking forward to asking you questions in the future. Jimmy Bagley, IA
• Wonderful service, prompt, efficient, and accurate. Couldn't have asked for more. I cannot thank you enough for your help. Mary C. Freshfield, Liverpool, UK
• This expert is wonderful. They truly know what they are talking about, and they actually care about you. They really helped put my nerves at ease. Thank you so much!!!! Alex Los Angeles, CA
• Thank you for all your help. It is nice to know that this service is here for people like myself, who need answers fast and are not sure who to consult. GP Hesperia, CA
• I couldn't be more satisfied! This is the site I will always come to when I need a second opinion. Justin Kernersville, NC
• Just let me say that this encounter has been entirely professional and most helpful. I liked that I could ask additional questions and get answered in a very short turn around. Esther Woodstock, NY
• Thank you so much for taking your time and knowledge to support my concerns. Not only did you answer my questions, you even took it a step further with replying with more pertinent information I needed to know. Robin Elkton, Maryland

• ### Mike

#### Satisfied Customers:

1425
Licensed Master Electrician - OnQ Certified Data Voice Audio Video Installer
< Last | Next >

### Mike

#### Satisfied Customers:

1425
Licensed Master Electrician - OnQ Certified Data Voice Audio Video Installer

### Jason

#### Satisfied Customers:

3871
Over 20 years of experience in all types of installations, troubleshooting, and repairs.

### Mike G.

#### Satisfied Customers:

6511
Proven Professional 46 years Experience

3264

### Kevin

#### Satisfied Customers:

2371
29 years as a Licensed Electrical Contractor in Illinois, 5 year college Electrical Instructor, Former Electrical Inspector, Diploma in Digital Electronics, Former Illinois Licensed Home Inspector

### electrifier

#### Satisfied Customers:

1458
Electrical contractor and electrical inspector for over 24 years with phone and networking expertise