Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > Electrical

CLICK HERE AND JOIN OUR COMMUNITY TODAY...IT'S FREE!

Reply
 
Thread Tools Search this Thread Display Modes
Old 08-19-2009, 11:03 PM   #16
Registered User
 
Termite's Avatar
 
Join Date: Apr 2008
Posts: 6,520
Share |
Default

Are A & B ever marked


Nap I was trying to gently question Johnnyboy's reasoning for the apparent white labeling of a phase conductor, which most of us know is incorrect. I didn't feel that just slamming someone for a what appears to be a misstep was the appropriate course of action, because this is a friendly forum for the most part.

I thought that was a nicer approach than blatantly picking someone's words apart.

Termite is offline   Reply With Quote
Old 08-22-2009, 06:32 PM   #17
Member
 
Join Date: Jun 2009
Location: San Diego, CA
Posts: 195
Default

Are A & B ever marked


Out of curiosity, how is the CT grounded? At the house I can see the ground wire from the plumbing to the neutral bar. But at the utility pole there are no conductors running down to the ground, so unless there is something internal to the pole, it must be grounded at one of the adjacent poles down the line. There are also guy wires on this pole because it is at the end of a line. Are the guy wires the grounds?
tns1 is offline   Reply With Quote
Old 10-22-2009, 03:00 PM   #18
Member
 
Join Date: Jun 2009
Location: San Diego, CA
Posts: 195
Default

Are A & B ever marked


OK so what about colors and terminology?
If the CT has terminals X1,X2,X3 as hot,neutral,hot, is there a standard association that X1 is always A, X3 is B or is this arbitrary?

I see some SER cables have completely different color scheme. Some with white stripes, some with blue stripes, etc. Is there some standard scheme to decide which of these will be X1, which will be X3?

I can see that my new panel uses black wire for both hots and these two lugs have no special marking, so it looks like the connection decision for the SER here is arbitrary. Electrically it should make no difference, but I am trying to find out if the code requires some consistency such as:

X1 always connects to the SER blue wire, which always connects to panel lug A, which always joins to a red marked wire, or if these associations are all random?
tns1 is offline   Reply With Quote
Old 10-22-2009, 07:52 PM   #19
Idiot Emeritus
 
Join Date: Mar 2008
Location: Fernley, Nevada (near Reno)
Posts: 1,596
Default

Are A & B ever marked


The secondary of a single phase pad mount transformer is usually marked X1, X0, and X2. X0 is always bonded to the frame, and is the neutral. X1 and X2 are both hot. It doesn't matter at all which one goes to which lug in the meter base or the panel. I've never seen a line crew intentionally connect X1 to the left side of the meter base.

The secondary of a single phase pole-mount transformer is usually marked X1, X2, and X3. All 3 are isolated from the frame. If the transformer is used for a 120/240 single phase service, X1 is one of the hots, X2 is the neutral, and X3 is the other hot. X2 is also connected to the pole ground.

If the pole mount transformer is used in a 3 transformer bank to make a 4 wire wye, it is re-connected internally so that 120 volts appears on X1 and X3. X2 is not used at all. The result is a 120/208 3 phase 4 wire wye.

The secondary is actually two separate 120 volt windings. When they are connected in series, one end of both windings is connected to X2, thus it is the center tap. When they are connected in parallel, they are both connected to X1 and X3.

Pad mount transformers are different. If 3 phase is needed, a 3 phase transformer is installed. If it's a wye, it is marked X0, X1, X2, and X3. X0 is always the neutral, and is always bonded to the frame. If it's a delta, it is marked X1, X2, X3, and X4. X4 is the neutral, but it isn't bonded to the frame. The reason is because if it is used as a 3 wire grounded B (sometimes called a corner grounded system), X4 isn't connected at all, and X2 is grounded. In a 4 wire delta system, X4 would be grounded.

Single phase transformer connections are very simple, the only one that matters is the neutral. 3 phase ones are a bit more complex, all 3 (or 4) must be connected correctly.

Rob
micromind is online now   Reply With Quote
Old 10-22-2009, 09:15 PM   #20
nap
You talking to me?
 
nap's Avatar
 
Join Date: Dec 2007
Location: sw mi
Posts: 5,407
Default

Are A & B ever marked


Quote:
Originally Posted by micromind View Post

Pad mount transformers are different. If it's a delta, it is marked X1, X2, X3, and X4. X4 is the neutral, but it isn't bonded to the frame. The reason is because if it is used as a 3 wire grounded B (sometimes called a corner grounded system), X4 isn't connected at all, and X2 is grounded. In a 4 wire delta system, X4 would be grounded.
b
rob; you lost me with the X1, x2, x3, x4 on a delta transformer or you simply did not explain something very well.

the only time you will have 4 wire delta AND a neutral is if you have a center tapped (high leg) connection. (well, the closest thing to being an actual neutral anyway) but from what I recall, no X4. Only x1,x2,x3,x0. Could be wrong on that point though. there are a few spare holes but I do not remember seeing one marked x4. If it was a transformer designed to be field connected wye or delta, then I could see the x4 but not unless.

With a straight delta, the 4th wire would be a ground. No neutral or grounded conductor. (don't find many ungrounded delta's anymore, especially new installs) (x4 superfluous if included)

In a corner grounded delta, x1, x3 hots, x2 grounded . If the grounding and grounded conductors are bonded in the transformer, there would be no 4th wire to the panel. If not bonded in the transformer, 4th wire is grounding conductor. No X4. (superfluous if included)

don't want to get into an argument about the last situation. I have seen it both ways and been required to do it both ways by various entities. Nobody seems to understand it well enough to have it the right way/

what say ye?
nap is offline   Reply With Quote
Old 10-22-2009, 11:22 PM   #21
Idiot Emeritus
 
Join Date: Mar 2008
Location: Fernley, Nevada (near Reno)
Posts: 1,596
Default

Are A & B ever marked


I think that the main reason they don't use X0 on deltas is to avoid confusion with wyes. If I see a transformer that has X0, I assume it's a wye. If it has X4, it's almost certainly a delta. X4 is usually the center tap of one of the secondaries. Usually X3 is the high leg, but not always.

I guess another giveaway would be that no bushing is bonded to the frame. Every wye I've seen has X0 bonded to the frame. Deltas do not. This makes the transformer more versatile, it can be used for either a 4 wire (with high leg), or a 3 wire (grounded B). Just bond the appropriate bushing.

I agree, there are very few grounded B systems in use these days, most of the ones I see are 480 anyway. I don't even know if the local POCO will connect a new service that's grounded B.

I hadn't thought of this before, but it's completely possible that different localities use different configurations. There could also be a difference between dry-type and oil-filled.

It's been a long time since I've connected a dry-type transformer with a delta secondary, and several years for an oil-filled one. Maybe my memory is not so good anymore.

Rob
micromind is online now   Reply With Quote
Old 10-23-2009, 09:58 AM   #22
CDH
Member
 
Join Date: Aug 2009
Posts: 40
Default

Are A & B ever marked


Quote:
Originally Posted by tns1 View Post
For single phase residential, are the utility feed wires ever marked A & B?
It shouldn't matter electrically, but I figured I'd ask anyhow.
Sometimes single phase services are paralelled ie more than 1 conductor to the can or panel and you will usually find red tape on the hotlegs tied together on one side of the can as they have been ohmed out to keep from cross phasing so yes occasionly you will find single phase residential sevices that are color coded for that reason. Someone stated in an earlier post that it was illegal to put white tape on a hotleg and that is probably the case on the customers side of the meter, but we lineman mark 3phase services a lot of the time red,white blue as that is the colors that are coming out of a phase rotator, where I work we signify the high leg with blue tape even though most inside electricians mark their side orange as I believe is the NEC code, anyhow it is done differently depending on the region of the country you are in as I have worked storms all over the place and know first hand.

CDH is offline   Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Liquidtight Metallic Conduit to Hot Tub Jacques411 Electrical 9 07-15-2009 11:09 AM
Replacing Toggle Switch with Rocker Switch dogsitter Electrical 8 07-04-2009 05:24 PM
Cable Size for Sub Panel vs chart jamiedolan Electrical 5 11-09-2008 01:30 PM
How Does A Double Pole Circuit Breaker Trip? shadowx360 Electrical 2 07-09-2008 02:44 PM
Do canned lights overheat? Not Sure Electrical 14 12-27-2006 07:44 AM




Top of Page | View New Posts

Copyright © 2003-2014 Escalate Media. All Rights Reserved.