VFD?s & Building Wire

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Jraef said:
One important point is that you have not said where the VFDs are going to be located; at the line source or near the pumps. In other words, is the 50' before or after the VFDs? If it is after, and the VFD output wires are in the same conduit, you are asking for trouble if they are not properly shielded; the VFD outputs will induce on each other and cause you no end of headaches, likely ending in frying the transistors one one or both drives.
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The VFD?s will be 50? before the pumps, and the existing pump circuits share a 1 ?? PVC that includes EGC from source to destination.
 
weressl said:
The motors are in a Class I, Division 1 location? They should NOT be driven by an ASD unless the motors are rated for it AND will be operated within the parameters speified.

Otherwise look in the drive specifications for wiring restriction. THHN in conduit should be OK.
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Yes these pumps are grinders in a C1D1. What's an ASD? I certainly hope the pumps were qualified for a VFD before this stage -- but I'm not sure -- I'm going to know soon [I-YI-YI]
 
Jraef said:
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The point about checking whether that grinder pump can be run from a VFD is a very good one. Grinder pumps are often expected to provide high starting torque, just in case they have to "munch" something, shall we say, inappropriate(?), on start up. Without over sizing, non-vector VFDs (and even many cheap-o vector versions) will effectively limit starting torque.
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All very well said!

Can't a VFD allow this starting torque though and couldn't it totally sense all required?

Is this a ratio to output question or the motor spin's to fast for proper tech or again and output/ QA problem ?

I don't know, just wondering!
 
tryinghard said:
The VFD?s will be 50? before the pumps, and the existing pump circuits share a 1 ?? PVC that includes EGC from source to destination.
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Two sets of unshielded VFD output conductors in a common PVC conduit will probably create problems.
 
steelersman said:
Isn't the EGC good enough to drain any stray voltages or currents?
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I'ts not a matter of stray voltages or currents, but the high-frequency, chopped wave RF field created in the wiring by a VFD. And having the fields of two drives side by each will affect both drives and motors, with possible release of smoke from motors and drives. :)

Need proof of the RF a VFD generates? Try to operate a portable radio close to one or it's motor, doesn't matter if it's AM or FM, you'll only get a lot of static. :)
 
mxslick said:
I'ts not a matter of stray voltages or currents, but the high-frequency, chopped wave RF field created in the wiring by a VFD. And having the fields of two drives side by each will affect both drives and motors, with possible release of smoke from motors and drives. :)

Need proof of the RF a VFD generates? Try to operate a portable radio close to one or it's motor, doesn't matter if it's AM or FM, you'll only get a lot of static. :)
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interesting. So basically you need to keep each set of wires in it's own conduit. But what about shielding it?
 
mxslick said:
I'ts not a matter of stray voltages or currents, but the high-frequency, chopped wave RF field created in the wiring by a VFD. And having the fields of two drives side by each will affect both drives and motors, with possible release of smoke from motors and drives. :)

Need proof of the RF a VFD generates? Try to operate a portable radio close to one or it's motor, doesn't matter if it's AM or FM, you'll only get a lot of static. :)
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So how does the shield clear or protect this action?

Does one pump circuit RF over to the other and somehow affect the others cycles? (Stupid is painful; ouch)
 
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To answer both questions;

A properly grounded/bonded metallic raceway will usually provide adequate shielding for the motor wires and help mitigate the RF radiation.


Shielding is a complex subject actually, and my understanding is that the shield acts as a "choke" or "inductor" (the quotes mean loosely speaking) to the magnetic (which is more or less what RF is) field which helps to supress it. :)

And yes, the two pump's fields can react with each other, and create problems. A lot of VFD's actually sense the inductance and reactance of the motor and adjusts the output to help maintain speed/torque.

I did an install with two film projectors and found out the hard way that the motor leads had to be in separate metal raceways. :) (No smoke released, but I did have serious speed stability issues.)
 
I have seen many installations where multiple VFD outputs were put into the same conduit; every one of them ended in the destruction of the drives. The multiple frequencies and the HF components most likely induce voltages on each other. That happens all the time on the 3 output conductors of any drive, but because they are at the same synchronized frequencies, they cancel each other out. With more than one drive, they are never synchronized.

You can get highly shielded (for lack of a better term) VFD cables from people like Belden and Lapp. They have the 3 conductors triplexed and then covered with an overall shield, protected by a jacket. That shielding will contain any EM or RF signals from radiating at dangerous levels, the jacket protects the integrity of the shield. Any other endeavor will likely end in disaster.

As to torque, very good vector drives can be relied upon to deliver full STARTING torque, defined as 160% of FLT. But to do so, they must put out enough current, and for long enough to be effective. Most "pump drives" are designed for what are referred to as variable torque loads, meaning they are not expected to have to do something like delivering that kind of current, or if so, probably not for long enough.

The CL1 Div2 issue is a hot one too, not to be taken lightly and could in fact be a show stopper.

If you want to do this, you need the help of a drive integrator with very specific experience in applying VFDs to grinder pumps. This is not a run-of-the-mill application.
 
Jraef said:
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You can get highly shielded (for lack of a better term) VFD cables from people like Belden and Lapp. They have the 3 conductors triplexed and then covered with an overall shield, protected by a jacket...
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Looks like a Beldon 29501, & cut sheet for 29501, can be used. It’s only #14 but seems to be rated and sized as per NEC.

It’s also only .6 diameter so wire fill won’t be a problem, I’m probably going to suggest this cable.
 
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iwire said:
It could be a lot of things, for me it is often a small hole drilled in the low point of a raceway, a small cut in the bottom side of a gasket etc.

Check out 225.22
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aha. I guess I was duped by weressl. And here I thought it had something to do with a drain wire that is usually found inside sheilded cable.
 
tryinghard said:
Looks like a Beldon 29501, & cut sheet for 29501, can be used. It?s only #14 but seems to be rated and sized as per NEC.

It?s also only .6 diameter so wire fill won?t be a problem, I?m probably going to suggest this cable.
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Take a look here for the full line of Belden VFD cable. Before you order the 29501 get a price on Belden 29521. I recently ordered some of the Belden VFD cable in #6, #4, 1/0, and 2/0. I had my supplier price it out in the traditional series and the symmetrical ground type and the symmetrical ground was actually cheaper, along with the benefit of reduced common mode currents due to the symmetrical design. Also note that Belden likes to sell this cable in certain size reels only, but there are distributors out there who will provide cut lengths. I needed a 700 ft piece and Belden sells 500 ft and 1000 ft reels. It was actually cheaper to buy 1000 ft from Belden rather than a 700 ft cut length - just something to keep in mind.
 
drbond24 said:
ASD = Adjustable Speed Drive
VFD = Variable Frequency Drive

Same thing. Speed is varied by adjusting frequency.
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You can have an ASD on a DC system, but a VFD only works on AC.

ASD is the generic term. An ASD could be nothing more than pulleys and belts, although it general means something more complicated like an eddy-current contoller or a variable frequency drive.
 
jim dungar said:
You can have an ASD on a DC system, but a VFD only works on AC.

ASD is the generic term. An ASD could be nothing more than pulleys and belts, although it general means something more complicated like an eddy-current contoller or a variable frequency drive.
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Good point. I've only messed with AC systems so I wasn't thinking it through all the way. I've always used the two interchangably. I'll have to be more careful with that in the future.
 
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