5 wire electrical versus 4 wire electrical

LockNut · Jul 28, 2016

Can someone please explain in layman's terms why 5 wire machine hookups are better (or not) than 4 wire and how you would physically hook up 5 wires to a machine that customarily uses only 4 wires.

Thanks,
Paul

bridgedog · Jul 28, 2016

Are you talking about single phase versus three phase? I don't think you have given enough information.

LockNut · Jul 28, 2016

Sorry, that's why I asked for help. My ignorance on the matter is profound, LOL. 3 phase for sure. This is for CNC machine tools.

Paul

Pariel · Jul 28, 2016

Three phase requires four wires: L1,L2, L3, ground.

What's the fifth wire going to?

Ziggy2 · Jul 28, 2016

Pariel said:
Three phase requires four wires: L1,L2, L3, ground.

What's the fifth wire going to?

The configuration you listed is for a delta configuration.

A star configuration uses a neutral wire. A 3ph version of center tapped 240. 120-neutral-120

adamm · Jul 28, 2016

I'll assume the 4 wires you are talking about are 3 "lines" plus the ground wire. For a 5 wire system the neutral wire is added.

If the machine is configured to use one ground, and 3 voltage lines, there is no need for the neutral. It just doesn't get hooked up. The purpose of the neutral is to provide a different voltage for a single phase load. For example, if you have a 208v/120v system, it will be 5 wire. From line to line on any of the three "line" wires, you would measure 208VAC. If you measure from one of the three lines to the neutral, it will read 120VAC. This allows wiring regular wall outlets, lights, etc from the same panel that is supplying 3 phase loads. In Canada it is common in industrial buildings to have 347 V lighting. That comes from using a 5 wire 575V system, and hooking the lights up between line and neutral.

So in short, one isn't better than the other. They just allow different voltages on one transformer so various devices can be wired up.

EJD3 · Jul 28, 2016

For strictly 3 phase, you only need the three legs of the incoming power, and a ground.
In some cases you may want to include a neutral. Most of the time the 4-wire system is sufficient for machinery, usually because there is a small control transformer with one side bonded to ground. This supplies a local neutral for low voltage control circuits (120vac). Control circuits like this use very little power and are contained entirely within the machine's systems.
In other cases, a neutral conductor would be pulled from the feeder panel to the machine, that's where the 5th wire comes in.

LockNut · Jul 28, 2016

Thanks everyone. That is what I was looking for. We are taking 23 machines to IMTS this year. McCormick Place electricians mandate 5 wire plugs for all installations. In 2012 we got hit for about $20K in extra charges because we used 4 wire plugs. That's what happens when you let a marketing guy make all the decisions.

Thanks, most appreciative,
Paul

Ziggy2 · Jul 28, 2016

LockNut said:
Thanks everyone. That is what I was looking for. We are taking 23 machines to IMTS this year. McCormick Place electricians mandate 5 wire plugs for all installations. In 2012 we got hit for about $20K in extra charges because we used 4 wire plugs. That's what happens when you let a marketing guy make all the decisions.

Thanks, most appreciative,
Paul

In this particular situation, they are mandating 5 wire plugs so that all situations are covered. There are a significant number of Asian and European machine tool builders that use a star or wye configuration for a two speed motor application.

If they didn't have the 5 wire services then these machines would have to use the ground as the neutral. Big no-no and code violation in addition to a safety hazard.

Pariel · Jul 28, 2016

How common is wye configuration for American machines?

I can't think of a single time I've seen or worked on a wye wired motor (although if the motor was working, one assumes I could walk past without noticing). I've certainly never designed something using wye (although I do remember it being mentioned by another engineer several employers back, now that I think about it).

Larry Dickman · Jul 28, 2016

Pariel said:
How common is wye configuration for American machines?

I can't think of a single time I've seen or worked on a wye wired motor (although if the motor was working, one assumes I could walk past without noticing). I've certainly never designed something using wye (although I do remember it being mentioned by another engineer several employers back, now that I think about it).

I've got an old engine lathe that's wired for Wye start/ delta run.

Ziggy2 · Jul 28, 2016

Larry Dickman said:
I've got an old engine lathe that's wired for Wye start/ delta run.

The wye start/delta run used to be very popular on large motors and or high inertia starting loads. The development of soft starters and VFDs has now made the old way obsolete.

Monarchist · Jul 28, 2016

LockNut said:
Thanks everyone. That is what I was looking for. We are taking 23 machines to IMTS this year. McCormick Place electricians mandate 5 wire plugs for all installations. In 2012 we got hit for about $20K in extra charges because we used 4 wire plugs. That's what happens when you let a marketing guy make all the decisions.

Thanks, most appreciative,
Paul

You said 'plugs', not 'sockets', and that you will be working into 5-wire sockets.

Surely worth checking further, but what I *suspect* I'd do to minimize hassle is run 5-wire cords & plugs, terminate the Neutral at the on-machine 'entrance' so it could be verified present, even if the machine didn't ever use it.

That just in case some munchkin feels they have to confirm it is 'there'.

I actually USE it here in my tiny shop. On-machine worklights, single-phase coolant pumps, PSU for electronic controls & accessories, etc. No need of separate 1-P 120 VAC cords to trip over.

More gain than pain, as five-wire keeps MY outlets simpler / more universal as well, even with but a handful of them in total. Fewer than half the count of what you are doing for one trade-show alone.

Bill

EPAIII · Jul 28, 2016

Exactly WHO "hit" you with those charges?

There are three things to consider when wiring machines: the local and national electric codes that apply in your location, the requirements of the machines that you are installing, and the electric service that is available.

I would start with the manufacturer's recommendations for the machine. If they recommend a five wire hook-up, then that is probably best. If they only recommend four wires, then that should work just fine. But the local service must support whatever you choose. And, of course, it all must be done in compliance with all applicable codes.

To my mind, that's it.

And yes, some machines may actually need both a ground and a neutral in order to operate properly, so five wires may be needed for lower Voltages. On the other hand, lower Voltages for control circuits can often be generated inside the machine with transformers. It just depends on how they were designed. Check the installation instructions for the individual machines.

A good, local electrician is your best friend here.

If that marketing guy wants to make the installation decisions, perhaps you should take over making the marketing decisions. See how he likes that.

LockNut said:
Thanks everyone. That is what I was looking for. We are taking 23 machines to IMTS this year. McCormick Place electricians mandate 5 wire plugs for all installations. In 2012 we got hit for about $20K in extra charges because we used 4 wire plugs. That's what happens when you let a marketing guy make all the decisions.

Thanks, most appreciative,
Paul

Monarchist · Jul 28, 2016

EPAIII said:
Exactly WHO "hit" you with those charges?
...

A good, local electrician is your best friend here.

Trade shows are always a "special case". Each.

The usual driver is overlapping authority, facility-owner, organizer, 'preferred' contractors, Unions, local inspectors, yadda, yadda. All-hands trying to simultaneously cover their arses, minimize effort, AND maximize fees for their portion. Not a one of 'em gives two shits in a windstorm about an individual exhibitor.

That, plus the organizer's wont to 'standardize' for minimal liability, handling time and effort on THEIR part leads invariably to odd 'shall // shalt-not' specs on everything from loading-dock access to lighting intensity to max headcount of both booth staff and setup and teardown munchkins at specified hours on scheduled days.

If I were to be back in that game, I'd probably carry TWO sets of cords per machine, do wotever the local 'Romans' asked. Power is but one of many 'details' that have to be addressed. Simplify, stay flexible wherever one can do.

Even when wrong, it is just NOT worth trying to boil that particular ocean, one venue after another.

Not as if it were a permanent factory-floor install anyway, so yah just rolls with it.

Bill

JST · Jul 28, 2016

Put the "standard" plug on the end and make them happy. Make sure it's the NEMA type they say.

What they want is NOT to have to supply outlets for every odd gizmo around. And they like extra money, of course. Since they run the venue, they can have a "policy" of "X" type wiring being standard, and a charge per outlet for anything else. As you found out, the charge can be large. NOTHING cheap in those places, they have you by the short hairs. The union in some places gets very bent if you do things like plugging something in, too.

Remember, they will also get you for $15 or some such crazy thing for a burger.... McCormick isn't close by downtown, and you have to be there, so where yah gonna go for electric OR burgers?

crij · Aug 2, 2016

Pariel said:
Three phase requires four wires: L1,L2, L3, ground.

What's the fifth wire going to?

Technically it is L1, L2, L3, Common, fifth wire would be chassis ground. Unfortunately most electrical panels (in the US, maybe different elsewhere) connect the common to the ground pin of the building so unless the site was wired for 5 wire 3 phase or 4 wire 220VAC Single (L1, L2, Common, Ground) it is just a duplication of the wire.

Ideally there would be a second ground pin located near the electrical panel for local ground, and the common would be connected to the pin closest to the mains. This will ensure if there is a surge that it limits the damage to the local area and not the whole site.

Rich C.

P.s. I guess I should have refreshed the page before posting, computer was sitting idle with page loaded for a few hours, and look a dozen or so replys which I duplicated, Sorry...

Jraef · Aug 2, 2016

My experience with setting up running machinery at trade shows is that if you ASK the exhibitor service people to actually plug in your stuff, it will not matter WHAT you have, theirs will ALWAYS be "different" and require them to do site changes, then charge you up the ying yang.

What I did, after the first time, is to ask them IN WRITING what THEY would provide, including the NEMA configuration number, then I would make my own adapters ahead of time. One time they told me they were going to provide their standard 20A 120/208V 3 phase 5 wire twist-lock outlets with configuration NEMA L21-20. So I made up my own adapters for them. When I got there, they used a 4 wire outlet, NEMA L14-20, which was what I actually NEEDED in the first place. So I asked them to repay me for the cost of the adapters and they refused. I then whipped out a copy of the email THEY SENT ME saying that it would be NEMA L21-20. Eventually the site manager offered me free carpet padding and extra chairs, but no cash.

steve-l · Aug 3, 2016

crij said:
Technically it is L1, L2, L3, Common, fifth wire would be chassis ground. Unfortunately most electrical panels (in the US, maybe different elsewhere) connect the common to the ground pin of the building so unless the site was wired for 5 wire 3 phase or 4 wire 220VAC Single (L1, L2, Common, Ground) it is just a duplication of the wire.

Ideally there would be a second ground pin located near the electrical panel for local ground, and the common would be connected to the pin closest to the mains. This will ensure if there is a surge that it limits the damage to the local area and not the whole site.

Rich C.

P.s. I guess I should have refreshed the page before posting, computer was sitting idle with page loaded for a few hours, and look a dozen or so replys which I duplicated, Sorry...

Rich,
You are incorrect. Never identify the fifth wire a second ground. It is dangerous. Under ALL electrical codes, ground is a safety circuit and should never carry return load current. Ground is also used as a reference and must remain quiet, which cannot happen if used as a return load current path, as all wires have some resistance. AC loads may be phase to phase or phase to neutral, never phase to safety ground. On principle, I never use a 4 wire connection, even if the equipment does not require single phase power because in the future, there very likely could be. In that light, I always include a neutral bus in the equipment.

Contrary to what EJD3 stated, control transformers are rarely connected to neutral. Control transformer primaries are almost always phase to phase, often with different strapping points for line voltage variations. Control transformer output voltages are not ground or neutral referenced. The secondary output is referenced only to itself, which if not realized, makes troubleshooting faults with a VOM impossible.

SAF · Aug 3, 2016

steve-l said:
Control transformer output voltages are not ground or neutral referenced. The secondary output is referenced only to itself, which if not realized, makes troubleshooting faults with a VOM impossible.

Steve, just so you know, here in the US, control transformer secondaries above 50V are required to be referenced to ground. Makes that troubleshooting easier sometimes...

SAF Ω

5 wire electrical versus 4 wire electrical

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