120 / 240V Service .... Assumed Delta????

AWinston

Member
Location
Murrieta, Ca
I am reviewing drawings from an Engineer that screwed up big time (undersized equipment, bad calcs etc). The incoming service is 120/240V 3PH-4W. Am I to assume that it is a delta system? I typically see 120/208V system. What made me question it is because the engineer has no loads on the B leg. I checked the new service order from the power company to bring the power into the building and it only says 600A 3PH 4W 120/240V.
 

infinity

Moderator
Staff member
Location
New Jersey
Occupation
Journeyman Electrician
Sounds like Delta to me. The B phase would only be used for 3Ø or 1Ø 240 volt loads.
 

Fulthrotl

~~Please excuse the mess. Sig under construction~~
I am reviewing drawings from an Engineer that screwed up big time (undersized equipment, bad calcs etc). The incoming service is 120/240V 3PH-4W. Am I to assume that it is a delta system? I typically see 120/208V system. What made me question it is because the engineer has no loads on the B leg. I checked the new service order from the power company to bring the power into the building and it only says 600A 3PH 4W 120/240V.
Delta. any single phase 120 volt loads on the B phase will get 208 off the high leg.
 

jaggedben

Senior Member
Is there supposed to be a standard difference in meaning between "120/240" and "240/120" in cases like this? That is, with one being split-phase and the latter being high leg delta?

I suppose it's fairly hopeless to expect everyone to know and remember it, I'm just asking.
 

mivey

Senior Member
Is there supposed to be a standard difference in meaning between "120/240" and "240/120" in cases like this? That is, with one being split-phase and the latter being high leg delta?

I suppose it's fairly hopeless to expect everyone to know and remember it, I'm just asking.
Yes, and Jim Dungar has mentioned it to me many times. The former being the single phase case and latter being the three phase case. I often just use 120/240 for three phase as well because it was industry standard utility notation for many years and old habits are hard to break.

Plus, the circumstances usually make it clear enough that I don't care anyway as long as the concerned parties know what is being discussed.
 

Jraef

Moderator
Staff member
Location
San Francisco Bay Area, CA, USA
Occupation
Electrical Engineer
Officially per ANSI standards, if you list the lower voltage first, it's supposed to denote single phase, if you list the higher voltage first, it denotes 3 phase.

So "120/240V" automatically SHOULD mean it is a single phase service, if it was listed as 240/120 (with nothing else), one should assume it is 3 phase. Best practice of course is to add "3 phase 4 wire" when talking 3 phase, just to make sure. Think about it, do we say "277Y480V" or do we call it "480Y277V"? That doesn't mean however that people have been doing it wrong for years...

Also, if it is 3 phase, it HAS to be a delta service with a center tapped leg to get 120V, there is no other way of doing it. If you had a 240V Wye service, the Phase-Neutral voltage would be 139V.
 

augie47

Moderator
Staff member
Location
Tennessee
Thanks for the replies. Now one more person can do it right.
Hopefully :D
but there's still us with age damaged brain cells. Mr. Dungar has corrected me more than once on proper terminology with regard to voltages and fault-current. I actually saved a few of his post, now all I have to to is remember where I saved them :) (I think he finally gave up on teaching me)

For other septuagenarians out there or those approaching, this will bring a smile:
https://www.youtube.com/watch?v=0wW-pVp7OZg
 
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