Olflex Cable Over-heating

[superdumpy]

Hi,

We are using a 4 * 50mm Olflex cable from a VFD via a Field switch Isolator to a HVAC Fan motor. The motor is running at 130amps Full Load Current.

We are experiencing very high temps at this field Isolator and I was wondering if anyone has come across this issue before with this cable.

Many thanks,
Thomas

 

[7anoter4]

Hi Thomas
The cable Olflex is a Lapp cable. I think is a Oil Resistant Motor Supply Cable for Large HP VFD Drives with UL & CSA TC Approval 3*1/0 AWG +8AWG.
According to Lapp catalog [see:]

http://www.lappusa.com/vfdselection.htm

For 50 hp motor 230 V FLC = approx. 130 A Lapp indicates this cable indeed.
As the core insulation is XLPE (cross linked polyethylene) the maximum temperature may reach 90 degree C[194 F].
If by "Field switch Isolator" do you mean an isolator [power] switch mounted on field then Field switch Isolator heating may be due to cable connection [ the cable lug is not properly fitted –in my opinion].
Also, if the cable is very warm indeed may be also a problem of the shield connection.
I think ,if there is no another problem, the shield has to be grounded only at one end.
Regards

 

[superdumpy]

Hi anoter,

Yes the field isolator is a switch for the motor before it enters the HVAC enclosure. I feel you are correct in suggesting the lugs. The Olflex I think is a type 7 stranded cable and I think the lugs used are for SWA which I think is a type 4 strand.

The high temps are occurring at the six connections of this Isolator. Would wrong lugs or crimps cause this problem?

Thanks,
Thomas

 

[7anoter4]

The SWA conductor of 50 sqr.mm dia is about 8.9 mm. The Olflex cable conductor may be a little more if it is circular stranded [9.4mm or compressed 9.15] .The usual lug inner dia is about 9 mm dia so I don't think the lug size is the problem. But the crimping may be a problem .Also the stud or the screw may be a problem.
If there is somewhere an aluminum-copper contact between cable lug and conductor or cable lug and the switch pad may be another problem.
Regards

 

[superdumpy]

Anoter,

When we changed the Isolator we re-lugged the cable therefore a crimping issue would mean two different Electricians crimped incorrectly. We have been onto the cable supplier and they are recommending different lugs. See attached data sheet. I have been trying to find out from them what the diffrence is with the lugs we are using and the ones in this sheet as they look identical.

 

[superdumpy]

Anoter,

Sorry wrong data sheet. See file for Lug data sheet.

 

[7anoter4]

First of all, I see your cable conductor is class 5 bunch-stranded [according to IEC 60228 standard] then the conductor diameter may be 11 mm indeed! So the lug, suitable for SWA 50 sqr.mm [8.9 mm] is too small.
Secondly, I cannot open your second attachment and I cannot see the lug. It is possible this lug is also long-tongue and the contact area is bigger.

 

[superdumpy]

Hi anoter,

The cable is 4core 50mm so I reckon we are too small with the SWA lugs as you state. Its possible that the Electricains have had to cut out some strands to get the core into the lug. Would this causing arcing and overheating in your opinion.

I'll attach that pdf again.

Cheers,
Thomas