Joined

·
188 Posts

1 - 20 of 23 Posts

Joined

·
188 Posts

Joined

·
15 Posts

I'll punt….120v and 3.84 KVA.

Joined

·
287 Posts

Joined

·
188 Posts

I figured it would look like homework but it's not...

I've been a member for 6 years lolll

Just not sure of this one... I'm trying to figure our how many kVA are left for a new application

Joined

·
188 Posts

Available current per line should be 83.3 A.

30 000 VA / (208 V x 1.732) = 83.3 A

If I measure 10 A on line A does that mean 73.3 A are available?

Joined

·
287 Posts

Yes, that is correct.

Available current per line should be 83.3 A.

30 000 VA / (208 V x 1.732) = 83.3 A

If I measure 10 A on line A does that mean 73.3 A are available?

Joined

·
188 Posts

Joined

·
188 Posts

Is it :

6000 VA / 208 V = 28.8 A

or

6000 VA / 2 lines = 3000 VA / 120 V = 25 A

If I add that charge to my panel via a single phase two pole breaker to the A and B circuits in addition to the already existing 10 A on phase A and 12 A on phase B what would be the current measured with a clamp meter on those two phases?

Joined

·
914 Posts

I'm a little rusty on this too, and I hope one of the experts will chime in.

It's been a while...

Question #1: The current measured on the secondary is at what voltage?

Question #2: Based on the readings what are the total kVA being used?

I don't think the 10A (A), 12A (B), and 10A (C) tells the whole story as far as KVA is concerned. You would need to measure each load (not just the feeders) and find the VA per load, then add that up.

3 phase: 208V x A x 1.732

1 phase: 208V x A

Total VA

I think?

It doesn't matter if the loads are 120, 208 or 3Ø, the transformer in question is good for 83.3 amps per phase. Neutral current doesn't matter, only phase current.

Is it :

6000 VA / 208 V = 28.8 A

or

6000 VA / 2 lines = 3000 VA / 120 V = 25 A

If I add that charge to my panel via a single phase two pole breaker to the A and B circuits in addition to the already existing 10 A on phase A and 12 A on phase B what would be the current measured with a clamp meter on those two phases?

Joined

·
188 Posts

But from what I understand, to compare apples with apples the 83.3 A is associated/relative to 120 V.It doesn't matter if the loads are 120, 208 or 3Ø, the transformer in question is good for 83.3 amps per phase. Neutral current doesn't matter, only phase current.

Therefore I'm guessing loads need to be converted to 120 V if I want to do any sort of calculation in regard to current per line.

For example, if I want to know the theoretical value that would be measured with a clamp meter after adding a load.

Current is current regardless of voltage. You have 83.3A per phase, regardless of if you hook it up LL (208V) or LN (120V).Some at my work believe that the original clamp meter readings (10A, 12A and 10A) are at 208V.

How can I prove that they're at 120V?

Since you state it is 208V, why would you hook it up to 120V?If I add a 6 kVA charge with 208 V single phase input power, how much would that pull on each line?

Is it :

6000 VA / 208 V = 28.8 A

or

6000 VA / 2 lines = 3000 VA / 120 V = 25 A

Joined

·
188 Posts

Tell me if I'm right...Current is current regardless of voltage. You have 83.3A per phase, regardless of if you hook it up LL (208V) or LN (120V).

Since you state it is 208V, why would you hook it up to 120V?

Let's say I have 30 kVA and therefore 83.3 A available per line/phase

Current = 6000 VA / (208 x 1.732) = 16.7 A

I therefore have 66.6 A left on each line

Current = 6000 VA / 208 = 28.8 A

I therefore have 54.5 A left on line A and B and 83.3 on line C

Current = 6000 VA / 120 V = 50 A

I therefore have 33.3 A left on line A and 83.3 A on line B and C

Joined

·
188 Posts

I'm trying to figure out the right way of calculating amps per line being usedBut you already stated that you are using option B (6kVA 208V 1p). What is the question?

Joined

·
4,154 Posts

Read AK Sparky's post CURRENT IS CURRENT, the measured current at the transformer terminals is the current the transformer is seeingI'm a little rusty on this too, and I hope one of the experts will chime in.

I don't think the 10A (A), 12A (B), and 10A (C) tells the whole story as far as KVA is concerned. You would need to measure each load (not just the feeders) and find the VA per load, then add that up.

3 phase: 208V x A x 1.732

1 phase: 208V x A

+ 1 phase: 120V x A

Total VA

I think?

Joined

·
188 Posts

I finally got it while writing the following post:Read AK Sparky's post CURRENT IS CURRENT, the measured current at the transformer terminals is the current the transformer is seeing

Let's say I have 30 kVA and therefore 83.3 A available per line/phase

Current = 6000 VA / (208 x 1.732) = 16.7 A

I therefore have 66.6 A left on each line

Current = 6000 VA / 208 = 28.8 A

I therefore have 54.5 A left on line A and B and 83.3 on line C

Current = 6000 VA / 120 V = 50 A

I therefore have 33.3 A left on line A and 83.3 A on line B and C

Thanks guys

Exactly correct.I finally got it while writing the following post:

Let's say I have 30 kVA and therefore 83.3 A available per line/phase

Option A : If I add 6000 VA @ 208/3 phases (3 line wires)

Current = 6000 VA / (208 x 1.732) = 16.7 A

I therefore have 66.6 A left on each line

Option B : If I add 6000 VA @ 208/1 phase (2 line wires)

Current = 6000 VA / 208 = 28.8 A

I therefore have 54.5 A left on line A and B and 83.3 on line C

Option C : If I add 6000 VA @ 120/1 phase (1 line wire + 1 neutral)

Current = 6000 VA / 120 V = 50 A

I therefore have 33.3 A left on line A and 83.3 A on line B and C

Thanks guys

1 - 20 of 23 Posts

Join the discussion

Electrician Talk

A forum community dedicated to professional electricians, contractors, and apprentices for residential and commercial work. Come join the discussion about trade knowledge, tools, certifications, wiring, builds, scales, reviews, accessories, classifieds, and more!

Full Forum Listing
Recommended Communities

Join now to ask and comment!