VFD?s & Building Wire

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tryinghard

tryinghard

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California
I?m involved with a project that has two 5hp 3ph pumps that are currently circuited with #10 THHN cu building wire, running about 50? from source to termination box. Apparently these pumps are too fast so rather than downsize the pump drives are being installed.

The existing pump motor circuits share a 1 ?? conduit with two TP?s (4 #12?s, a pair for each pump). An installer is concerned that the pump circuits should be replace with shielded cable with the use of the drives.

I really don?t understand how controlling the frequency can cause problems. Is this really necessary, can these operate trouble-free without using shielded cable for the pump circuits?
 
I have installed a lot of drives in this size range and have never used anything other than normal building wire. Most of the runs would be well over 100' and have not experienced any issues. We do not use line or load reactors either.
 
The few I?ve done are building wire also. These circuits route through an EYS into a C1D1 environment as well. I wonder if shielded cable is needed if the pump circuits ran with signal cable like 4/20?
 
tryinghard said:
The few I?ve done are building wire also. These circuits route through an EYS into a C1D1 environment as well. I wonder if shielded cable is needed if the pump circuits ran with signal cable like 4/20?
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when we wire the controls to the vfd's we use shielded cable (18-2 and 18-3) but only for the analog signals. The digital or binary signals don't need to be shielded cable.
 
We use standard buliding wire but do use load reactors as suggested by the drive & pump motor mfg. I do not remember where I read it but this is more important for motors operating at 480v than 208. A SQD unit we used suggested a line reactor and shut down twice before we got it installed. No problems since.
 
We did two submersible pumps for a grocery that used them for compressor cooling. The pumps alternate every 24 hrs, the second comes online as needed with both pumps then running at reduced speed to maintain pressure. The pumps then change lead/lag after running at min rpm for ___ minutes. A certain amount of water is required to run past a submersible to ensure cooling so don't let them run to long at minimum rpm unless you are sure enough volume of water is flowing.

The store went from broken water lines under a concrete parking lot, prematurely failed heat exchangers, and mad dashes for the compressor room when the pumps quit, to virtually no problems in the last three years.
 
You can do this and get away with it most of the time. 50' yea you should be fine even as stated in another reply 100' ok, but we have had a situation here at work where are motors were located 100' to 200' away from our drive. New installation and a week later were dropping motors like crazy. Not very happy about this at all. We ended up installing load reactors to remedy the problem but shielded cable may have helped avoid this problem. Look at the speeds your operating the drives on also I believe you stated the pumps were running too fast and you wanted to slow them by half. Slowing the pump below 60hz poses a heating issue also.
 
ptonsparky said:
We use standard buliding wire but do use load reactors as suggested by the drive & pump motor mfg. I do not remember where I read it but this is more important for motors operating at 480v than 208. A SQD unit we used suggested a line reactor and shut down twice before we got it installed. No problems since.
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These pumps are 240v and are grinders for a lift station, they alternate but can come on together if needed (although if these are currently to big this action won't likely happen).

Maybe I should verify the drive and or line reactor with the pump manufacture, I would think they would qualify its compatibility with VFD's?

Would the drive manufacture have direction regarding circuitry, I don't remember seeing this on the few I've done?
 
tryinghard said:
These pumps are 240v and are grinders for a lift station, they alternate but can come on together if needed (although if these are currently to big this action won't likely happen).

Maybe I should verify the drive and or line reactor with the pump manufacture, I would think they would qualify its compatibility with VFD's?

Would the drive manufacture have direction regarding circuitry, I don't remember seeing this on the few I've done?
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It wouldn't hurt to ask. It would be in their best interest to make sure whatever you buy from them works as well as possible so you're happy with it. A phone call now might save you some trouble down the road.

Just don't ask the cable manufacturer. :) They'll have you buying high dollar VFD cable whether you need it or not.
 
We were asked to investigate why all the audio and video feeds plus the phone system gets knocked out each time they flush the toilet.

It turns out a 1.5 hp. v.f.d. was used for the well pump motor.

The distance between drive and motor was greater then 200'(standard wire).Drive was relocated closer to well,problem disappeared.:smile:
 
You maybe having bigger problems

You maybe having bigger problems

tryinghard said:
The few I?ve done are building wire also. These circuits route through an EYS into a C1D1 environment as well. I wonder if shielded cable is needed if the pump circuits ran with signal cable like 4/20?
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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.
 
tryinghard said:
These pumps are 240v and are grinders for a lift station, they alternate but can come on together if needed (although if these are currently to big this action won't likely happen).

Maybe I should verify the drive and or line reactor with the pump manufacture, I would think they would qualify its compatibility with VFD's?

Would the drive manufacture have direction regarding circuitry, I don't remember seeing this on the few I've done?
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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.

My suggestion would be to locate the VFDs as close to the pumps as possible, preferably after that junction box so that each VFD output will have its own separate conduit.

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.
 
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.

My suggestion would be to locate the VFDs as close to the pumps as possible, preferably after that junction box so that each VFD output will have its own separate conduit.

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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Depending on the type it may even be a constant torque application. The area classification also remains a question.
 
tryinghard said:
And I would have guessed this opposite, you mean controls like floats?
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No I'm referring to VFD's that control the speed of air handlers and we wire the controls into the VFD's from Johnson Controls panel. There's an analog output for the speed signal, a digital output to command the air handler on, a digital input for status (which simply is a NO contact on a CT doughnut that we install to let the Johnson Controls monitoring system know whether the fan motor is running or not, an analog input into the VFD from an airflow sensor which is installed right after the fan, another analog input from a static pressure sensor inside the air handler, and a safety circuit. All of these wires are 18 guage. Only the analog signals are required to be shielded.
Also FYI we aren't the electrical contractor on this job, (or any other jobs for that matter) although we are all electricians. We strictly do Johnson Controls' work.

Also the electrical contractor on this job doesn't run their power in shielded cable, nor have I ever seen any VFD's with the power being shielded. I've always seen just regular THHN conductors in EMT.

After reading JRAEF's post I realized that it could be possible for interference to occur the way he described. But in all of the applications I've seen, each drive had it's own conduit going to it's own motor, so there was no mixing of conductors from other sources or circuits. Also these drives are always located as close as possible to the motors they serve (probably an average of 50 feet of conduit from VFD to motor).
 
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Part of the issue with shielded wiring comes from the one instruction manual being written for the entire world.

The intent of the shielding requirement is primarily to reduce occurrence of the conductors acting as broadcast antennas for EMI.

If metallic raceways, containing normal building wiring, are bonded to ground they will provide the required shielding. If non-metallic raceways or cables are used the conductors will need to be shielded.
 
jim dungar said:
Part of the issue with shielded wiring comes from the one instruction manual being written for the entire world.

The intent of the shielding requirement is primarily to reduce occurrence of the conductors acting as broadcast antennas for EMI.

If metallic raceways, containing normal building wiring, are bonded to ground they will provide the required shielding. If non-metallic raceways or cables are used the conductors will need to be shielded.
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You also need it to drain any stray voltages or currents so as not to interfere with the delicate signals.
 
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