# 115VAC 3-Phase

#### ianmurphy

##### Member
I am an electrical designer currently working on the design of a ship. I am familiar with buildings, new to ships. Apparently, there are 115VAC 3-phase panels on this ship, I tried to convince my colleagues that that sort of system doesn't exist but apparently it does. I have been told the ship’s power provides 115VAC 3-phase, delta (3-wire, no neutral) where any line-to-line combination provides 115VAC. Can someone school me on this? I cant find any explanations online.

#### winnie

##### Senior Member
It is not a common voltage used on land, and the rules and electrical codes applied to ships are very different from those used for structure wiring.

Conceptually it is no different than an industrial 480V ungrounded delta, simply done at a different voltage. Vab is 115 volts. Vbc is 115 volts and 120 degrees out of phase with Vab. Vca is similarly 115V and 120 degrees out of phase with Vab and Vbc.

-Jon

#### Jraef

##### Moderator
Staff member
Never heard of it and it makes no sense. You get zero benefit of running the 3 phase distribution system by not taking a vantage of the higher voltage phase-to-phase.

I’d bet that this is coming from someone unfamiliar with 3 phase systems and they really have a 208Y120 system, but that person only reads the phase to neutral voltages.

#### winnie

##### Senior Member
Take a look at this couple year old thread:

#### jim dungar

##### Moderator
Staff member
Never heard of it and it makes no sense. You get zero benefit of running the 3 phase distribution system by not taking a vantage of the higher voltage phase-to-phase.

I’d bet that this is coming from someone unfamiliar with 3 phase systems and they really have a 208Y120 system, but that person only reads the phase to neutral voltages.
No.
120V ungrounded delta systems exist on board ships, especially military ones. Think of the advantage for continuing power deliver should one conductor become accidentally grounded.

#### wwhitney

##### Senior Member
120V ungrounded delta systems exist on board ships, especially military ones. Think of the advantage for continuing power deliver should one conductor become accidentally grounded.
So are all the loads 2-wire 120V, or are there significant loads that benefit from being supplied by 120V delta? Because for the former, I would think a 120/240V split phase ungrounded system would be more efficient. Although it would require 240V insulation rather than 120V insulation, if that's a significant issue.

That is, for 1 amp on each conductor, the 3-wire 120V delta delivers 120 * sqrt(3) = 208VA, while the 120/240V split phase delivers 120 * 2 = 240 VA (and has 0 amps on the neutral).

Cheers, Wayne

Edit: 120/208V 3-wire would also deliver 240VA while limiting the L-L voltage to 208V. And of course 208Y/120V 4-wire would deliver 360VA, with the highest VA/wire-amp so far.

#### b1miller

##### Member
115V 3 phase systems are very common on naval ships. I wired up many way back in my marine electrician days. They are typically used for compartment lighting and receptacles. Almost always fed from a bank of three 480V to 115V single phase transformers. If a single transformer failed then at least they had the other 2 phases still working. They were feeding three phase 115V fuse panels. The Navy did not use circuit breaker panels for those circuits. A severe shock from a torpedo or other hit could trip a circuit breaker.

#### petersonra

##### Senior Member
Never heard of it and it makes no sense. You get zero benefit of running the 3 phase distribution system by not taking a vantage of the higher voltage phase-to-phase.

I’d bet that this is coming from someone unfamiliar with 3 phase systems and they really have a 208Y120 system, but that person only reads the phase to neutral voltages.
I just did a project for a test stand that needed 3 phase 120 V power. I wired up 3 480/120 V single phase transformers to get the 3 phase 120 V.

#### GoldDigger

##### Moderator
Staff member
115V 3 phase systems are very common on naval ships. I wired up many way back in my marine electrician days. They are typically used for compartment lighting and receptacles. Almost always fed from a bank of three 480V to 115V single phase transformers. If a single transformer failed then at least they had the other 2 phases still working. They were feeding three phase 115V fuse panels. The Navy did not use circuit breaker panels for those circuits. A severe shock from a torpedo or other hit could trip a circuit breaker.
If you started with a three phase delta, the losing one ttransformer as open circuit you would still have all three phases, just as an open delta. If any feed transformers are involved, losing one primary phase could also still give you all phases as open delta. It all comes down to the generator, where you could still lose one phase open and feed alll three phases.

#### ianmurphy

##### Member
115V 3 phase systems are very common on naval ships. I wired up many way back in my marine electrician days. They are typically used for compartment lighting and receptacles. Almost always fed from a bank of three 480V to 115V single phase transformers. If a single transformer failed then at least they had the other 2 phases still working. They were feeding three phase 115V fuse panels. The Navy did not use circuit breaker panels for those circuits. A severe shock from a torpedo or other hit could trip a circuit breaker.
Thanks for the info. Real basic question, but how would you wire up a 120V receptacle to a delta system like this? would you just use any two of the phases?

#### tom baker

##### First Chief Moderator
Staff member
From my navy days there was a fuse in each line. Charlie B would kno, was was navy electrical engineer on the Nimitz

#### retirede

##### Senior Member
Thanks for the info. Real basic question, but how would you wire up a 120V receptacle to a delta system like this? would you just use any two of the phases?

Yes

#### RichB

##### Senior Member
No.
120V ungrounded delta systems exist on board ships, especially military ones. Think of the advantage for continuing power deliver should one conductor become accidentally grounded.
correct--we didn't want to loose power to something vital in a combat scenario--Former EM1 78-87

#### Besoeker3

##### Senior Member
From my navy days there was a fuse in each line. Charlie B would kno, was was navy electrical engineer on the Nimitz
I know this is a bit off topic and I understand that you were in the navy. I wasn't but I did a few projects for ice breakers. mostly in Canada. The ones we did were 575V VSDs for me. At there power levels, 280kW or so, I can't imagine would be practicable at 115Vac.

#### topgone

##### Senior Member
I know this is a bit off topic and I understand that you were in the navy. I wasn't but I did a few projects for ice breakers. mostly in Canada. The ones we did were 575V VSDs for me. At there power levels, 280kW or so, I can't imagine would be practicable at 115Vac.
That's another animal you are talking about.
I agree with others. My previous employer bought an old power barge (a long time ago, US military 30 MW steam generator circa WW2) and all receptacle outlets were 115V.

#### Jraef

##### Moderator
Staff member
Learned something new today.