480V Wye Vs Delta Distribution Panels
480V Wye Vs Delta Distribution Panels
(OP)
Please help. I am a new engineer which explains the simple question. When purchasing a distribution panel to be fed by 480V delta 3 phase 3 wire is it okay to buy one rated for 480V wye 3 phase 4 wire? Are they always interchangeable? What differences would I have to look out for?
Thanks,
Thanks,






RE: 480V Wye Vs Delta Distribution Panels
RE: 480V Wye Vs Delta Distribution Panels
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: 480V Wye Vs Delta Distribution Panels
RE: 480V Wye Vs Delta Distribution Panels
But I believe the design and certification testing of the panel is the same for a grounded wye or ungrounded delta system. So the panel is not different. But some breakers may only be listed for 480/277V.
You can buy a 3-phase, 4-wire panel and use it on a 3-phase, 3-wire system. Just make sure the neutral bar is removed and the circuit breakers are rated for full voltage.
RE: 480V Wye Vs Delta Distribution Panels
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: 480V Wye Vs Delta Distribution Panels
RE: 480V Wye Vs Delta Distribution Panels
You also remove the UL listing and may get the installation red tagged.
RE: 480V Wye Vs Delta Distribution Panels
RE: 480V Wye Vs Delta Distribution Panels
respectfully
RE: 480V Wye Vs Delta Distribution Panels
RE: 480V Wye Vs Delta Distribution Panels
With 480V systems, SOME breakers are rated for 3ph 3 wire installations, some are not. Those that are not are called "Slash" breakers, because the ratings will say "480/277V", meaning that their interruption capacity was tested based solely on 4 wire systems where the maximum voltage to ground will be 277V. So therefore, SOME panelboards are rated for 3 Ph 3 wire installations, some are not. Breakers that are rated for 3 wire can be used on 4 wire installations, but not the other way around. Because of that, panels that are ordered for 3 wire installations have provisions that reject the installation of Slash breakers, and conversely when you buy a panelboard with the coding for a 4 wire bus, you cannot change it to be used on a 3 wire installation by removing the bus because you will be able to plug in Slash breakers that cannot be connected to 3 wire. Actually you CAn physically do it, but you are violating it's UL listing and subjecting yourself to liability.
So make sure of what you have and need, then specify it carefully.
RE: 480V Wye Vs Delta Distribution Panels
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: 480V Wye Vs Delta Distribution Panels
RE: 480V Wye Vs Delta Distribution Panels
RE: 480V Wye Vs Delta Distribution Panels
As I understand it, a slash breaker cannot be used for 3 wires equipment because it has to support line-to-line Voltage instead of just line-to-ground.
If I am right, then why do a 3W panel connected to a 4W solidly grounded system via a 3W feeder can use "slash rated" breakers?
RE: 480V Wye Vs Delta Distribution Panels
Think about a line-to-ground fault. If the system serving the panel is 4W solidly grounded, the highest voltage from phase to ground is 277V, regardless of whether or not there is a neutral carried to the panel. There is still a neutral-ground bond at the source. That situation doesn't change if there is a neutral carried to the panel on not.
RE: 480V Wye Vs Delta Distribution Panels
I was under the impression that slash rated breakers were only available in single pole configuration for this reason.
Comment?
respectfully
RE: 480V Wye Vs Delta Distribution Panels
On a grounded 4W system, the maximum voltage across any one breaker pole is the L-N voltage.
RE: 480V Wye Vs Delta Distribution Panels
It used to be that way, but IEC manufacturers trying to sell MCBs (Miniature Circuit Breakers) here in the US exploited that slash rating issue to make their products more "acceptable" to 480V users. You probably don't see it happening much in Canada because they don't have a 600V "slash" rating at all.
So they (we, because I now work for Siemens) are now selling 3 pole MCBs with 480/277V ratings on them. I for one try to educate the users on just what this means, but 99% of them don't want to hear it because they want the cheap price. I make my salespeople walk away from those customers, but most of my competitor's salespeople have no clue what it means and just sell them willy-nilly. I have even started seeing them being used as Main circuit breakers on control panels recently because several manufacturers have now come out with thru-door interlocking handle operators. It's a disaster waiting to happen in my opinion, but nobody seems to be listening.
RE: 480V Wye Vs Delta Distribution Panels
Special star for Jraef.
For the:
"I for one try to educate the users on just what this means, but 99% of them don't want to hear it because they want the cheap price. I make my salespeople walk away from those customers."
Regards.
Slava.
RE: 480V Wye Vs Delta Distribution Panels