If there is potential between them, breaker trip.

 

Wye or delta secondaries? Grounded?

 

If it's the same service and the phasing is the same between the 2 panels, no problems but the overcurrent protection would double.

The neutrals wouldn't matter as they are all connected together.

 

If it's the same service and the phasing is the same between the 2 panels, no problems but the overcurrent protection would double.

The neutrals wouldn't matter as they are all connected together.

He’s not talking about the same phase. He indicated two transformers. That’s why @splatz asked about wye, delta, and grounding.

 

I'd want to see that on a scope before I connect any money to it.

 

I don't think anything would happen, really.

There would be two separately derived systems, and I believe you mentioned only one neutral that would return to only the originating source.

Anyway, my opinion.

Andy.

 

I am talking about general commercial space, specifically highrise 208/120 and 480/277. Delta-wye.
I have seen neutrals crossed between emergency ltg/ generator branch and normal lighting branch in old exit lights and egress lights. (Lighting maintenance getting confused replacing ballasts probably.) I only became aware of these problems when working on panels where the feeder was locked out, but there was still current on the neutral. I’m not aware of that causing any problems in the branch ckt outlets, and those miswirings were 10-30years old.
There is always/often that 0.1a reading on the amp clamp when everything is turned off, and we call that a ghost reading, but the meter is reacting to something.
So this post is me thinking about how I would notice this type of miswire during a shutdown.

 

I am talking about general commercial space, specifically highrise 208/120 and 480/277. Delta-wye.
I have seen neutrals crossed between emergency ltg/ generator branch and normal lighting branch in old exit lights and egress lights. (Lighting maintenance getting confused replacing ballasts probably.) I only became aware of these problems when working on panels where the feeder was locked out, but there was still current on the neutral. I’m not aware of that causing any problems in the branch ckt outlets, and those miswirings were 10-30years old.
There is always/often that 0.1a reading on the amp clamp when everything is turned off, and we call that a ghost reading, but the meter is reacting to something.
So this post is me thinking about how I would notice this type of miswire during a shutdown.

Neutrals crossed is not what your first post was about. You said “what if two hots from different transformers were connected “

 

.1 amps is often from the resistance on the display screen for digital meters. My fluke always shows .1 amp even when clamped around a tree branch.........

 

So what do you think would happen if you did this? Two 208/120 wye secondaries, solidly grounded.

1. Same current flows on the load (same as if only one or the other was connected)
2. Double the current through the load
3. Dead short, breaker trips

 

1. Same current flows on the load (same as if only one or the other was connected)
2. Double the current through the load
3. Dead short, breaker trips

Spoiler: My guess

3. The centers of the wyes are bonded, there's going to be a low impedance path between them. So the two phases are in series then you jumpered them. BOOM

 

Could be dangerous if Panel A is LOTO and someone is working on panel A thinking that is is shut down but you will get a back feed from Panel B . As for the sine wave and time curve I leave that to the engineers.

 

Coming from the same source, the secondaries of two identical transformers will be in sync, same frequency, although shifted.

If the transformers are bonded the usual way, and someone doubled up the way I have in my drawing, the two windings are in series on the jumper / short - not in parallel, right? So the voltage will be 240VAC from A to A. Like @backstay pointed out it's like the center tap of a 240 winding on 240/120 residential service.

 

So if it's like this

both transformers ungrounded secondaries. Wired with both A-N in parallel.

Let's say that load is a 120 watt lamp. Does it draw 60W off each 120W total, or does it draw 120W off each 240W total (assuming that doesn't burn it out immediately).

I am thinking it's going to burn 120W as usual but I went back and forth on this.

 

40 years ago I could answer questions like this in my sleep. Now I just look at the hand drawn pictures. I remember back in the 1980s when I was working for another contractor, the local hospital had a 3500kva transformer burn out it was fed with 15,000 volts on the primary side and 480/277 on the output. The boss located 2 - 1600kva which we paralleled the two. We had some problems with union sabotage but after we fixed it we turned the 200 amp high voltage switch and the paralleling worked.

 

So if it's like this

View attachment 208285

both transformers ungrounded secondaries. Wired with both A-N in parallel.

Let's say that load is a 120 watt lamp. Does it draw 60W off each 120W total, or does it draw 120W off each 240W total (assuming that doesn't burn it out immediately).

I am thinking it's going to burn 120W as usual but I went back and forth on this.

120W.

same frequency, although shifted.

Are they necessarily shifted phase?

 

Same phase, but different xfmrs?

Makes one wonder?
How many wires does it take to make a phase?
Sounds like a job for a volt pen, would that tell you which transformer was the source?

 

 

How do you think it works for the Electric Utility when moving load from one substation breaker to a different substation breaker when performing a closed transition?

 

I wonder what we will come to, when AI learns everything from online, and has no way to differentiate between what parts of it are correct and which parts are not? I would assume that the ones that reference it as always factual, will become dumber. And consume large energy resources in the process.

 

In the city of Victoria We have a network downtown built by BC Hydro. there are 112- 500 KVA transformers connected together. it provides very high reliability but with a very high fault current. main breakers and fused disconnects must have at least 100KA interrupting capability. Calgary has 3 networks 120/208/277/480 and 347/600.
So in answering this question. it would work just fine.

 

I apologize if I received this answer.I did not read every post. But doing it the way the gentleman asked, wouldn't you need to do some specific current protection with fuses for each device?

 

It happens all the time it’s called the grid

 

Until you shut down the breaker in one panel and still have a hot on the load side. Besides, the OP talked about crossed neutrals then switched to doubled up hots. Two very different animals.

 

Yes, I have shut down panels and still had neutral current. Those memories just have me thinking about other situations like double fed hots in 3-phase facilities with multiple transfer switches, and how I could be prepared to recognize and troubleshoot.

Some places you hook up a circuit tracer and it’s all over the place.

I’ve dealt with double fed hots in residential single phase, and a also lot of tract houses where all the whites are wirenutted together in every jbox (then everything in the jbox is spraytextured and painted white.)

 

I concur with Micromind. As long as it is the same service, then all will be fine.