I'd like to correct some misconceptions/mistakes on this thread:
Hey everyone, I'm new here, but I've searched around and haven't been able to find an answer to my first question...
I'm moving my business into a new shop space which seems to have less electrical wiring than I'll need. The 1phase 240 is also on the opposite side of the shop than I'll need. So, here goes my question...
I have a 240v 3phase power box on the side of my shop that I want to run my 1phase 240v tools on (welder, tablesaws, etc.). It looks like this :
The outside of the box says:
"240v 3phase Delta
Compressor"
Now from what I've been able to gather the 3 hot wires out of phase without a ground or neutral wire is typical of the delta 3phase system. I know I can get 208v by using 2 legs of the 3phase, but where do I get my ground from? Do I create one with a ground spike or water line? If possible I would like to split this power off to a separate breaker box and run my 240v stuff off of it. How can I do this? Am I stuck wiring the existing 240 1phase across the shop to the other side where I need it? If I were ever to get 3 phase tools where can I ground them? Would I need to?
Thank you in advance for any time you put into this. Forums are a great way to share knowledge and I hope one day I can share mine.
Bryan Wiesendahl
There should ALWAYS be an EGC run with each circuit! Sometimes however, the conduit will be used as the EGC instead of a ground wire.
And, no you can't just "make" a ground with water pipe or ground rod. EGCs(aka grounds) and grounding electrode systems(ground rods, ufer, etc.) serve 2 different functions. EGCs are for clearing ground faults and grounding electrode systems are for grounding lightning strikes.
You CANNOT get 208v from a 240v delta. You will need a wye service if your equipment needs 208v or you can use buck/boost transformers.
Yes, you can take 2 legs of this branch circuit and use it for your 240v single phase loads!
The absence of a ground wire does not mean its definitively a delta service because PoCos do NOT feed a ground wire/EGC in the service drop. EGCs are only found on the load side of electrical services. The only way to know for sure what type of service u have is to check the voltage.
Now if this is just a sub-box off a 240V corner grounded delta three phase service you will have a grounded conductor some place to allow you to have 120V.
William....
The grounded phase conductor in a corner grounded delta WILL NOT give u/does not have 120v potential between it and another phase or ground. While the NEC says to label and treat it like a neutral with regards to coloring, disconnects, fuses/breakers, etc. it does not have the same 120v potential that a center tapped neutral does. This is because the neutral conductor in a corner grounded delta is also a phase conductor and does not come from the center tap on one of the transformers.
So, the 'neutral' grounded phase conductor has 240v(or 480v) potential between it and the other 2 phase legs and Ov potential to ground(because it is grounded)! 120v equipment will be fried if connected to the grounded phase conductor and another phase leg in a corner grounded delta!
There is several types of delta services- straight 3-wire delta(240v or 480v), corner grounded delta(240v or 480v), and center tapped/high leg delta which is 4 wire(always 240v/120v/208v between neutral and high leg).
http://www.electrical-contractor.ne...cs/177456/New_3_Ph_3_Wire_Corner_Grounde.html
I didn't see a ground anywhere in the 3 phase box. The shop is divided into 2 services; A single phase 100amp service I'm comfortable working in, and then this 200amp 3 phase 240v box. The 3 phase box is 3 wires in (blue, black and red) feeding a large switch, 3 inline fuses, then 3 wires out (blue, black and red) that terminate at 3 distribution blocks. Since there is no ground wire can I assume that this is a straight delta service without a corner ground? Would they have used the conduit (sounds really sketchy but I've heard of it) as a ground if it was corner grounded elsewhere?
NEVER ASSUME when it comes to electrical and electricity! U need to go to the service entrance/meter main and figure out what u have. Look for the feed wires coming in from the pole:
If u have 3 wires, then it could either be a regular delta or a corner grounded delta. To check if its corner ground, u need to measure the voltage between each phase conductor and ground such as the panel. If u get a reading of 0v from one of the phase legs to ground, then its a corner grounded Delta.
If u have 4 wires coming in, then one will be a center tapped neutral(120v). But most likely, since u have 2 services, this will be a 3-wire service.
Why is using conduit as an EGC sketchy? The conduit in most electrical systems is already bonded to ground via breaker panels!
Also, you are confusing different types of electrical services. If the service type is corner-grounded delta, then 1 of the 3 phase legs is your ground in a 3phase branch circuit.(see diagram in above link) It must be bonded to a ground bar in disconnects and panels and never have in-line fuses or breakers that could disconnect it! Since you said there are 3 inline fuses in the disconnect, you probably don't have a corner grounded delta. But many electricians have made the mistake of putting a fuse inline with a grounded phase conductor, so you should test the voltages in your system to make sure first!
The corner ground is for a grounded conductor or neutral. And it's normally done at the transformer, then they run in 4 wires. The Equipment ground is provided at your end, and they may be using the conduit to distribute it around. That raceway/wire way should be connected to a grounding electrode/system at some point. I don't really like to trust that method and I run a EQ. Ground wire in my wire ways and conduits.
I couldn't see the other tape on the wires. So it is possible that you have no wild leg, and there are three transformers feeding your system. Take a volt measurement between the legs and also to the ground and see if you have a high leg (about 200V to the EQ ground)
William...
A corner grounded delta was, is and will ALWAYS be 3-wires. Yo cant have 2 different neutrals(corner grounded neutral and center tapped neutral) in the same system.
Also, in a delta configuration, u could have 2 or 3 transformers. The 2 x-former setup is called an open delta. The high leg only matters if the service is 4-wire with a center tapped neutral. And the high leg is usually 208v to neutral.
If your setup is delta, then you have no neutral, and no provision for one probably. You might be able to use a transformer to create a neutral (1:1) with a center tapped secondary with the center tap being the neutral) but that transformer may be a bit expensive.
Actually, some types of delta services DO have a center tapped neutral that gives 120v between netral and 2 phase legs. Its called a high leg Delta. Theres other names for the high leg which are stinger, red leg, and wild leg.
If you have a separate single phase service, your 240 Volt Delta service is just that, with no "Wild Leg" or grounded corner of the Delta.
If there is no center tapped neutral, then yes, there would be no wild leg. However, you can have a grounded corner on a 240v delta service as long as its 3-wire and 1 phase leg is grounded! But unless this is a very old service, I doubt its corner grounded as utilities stopped providing this type of service eons ago!
Now if this is just a sub-box off a 240V corner grounded delta three phase service you will have a grounded conductor some place to allow you to have 120V.
on this thread even though it IS almost 2 years old.
Now I feel like a fool. I am usually one of the first to notice something like that.