Max length of control cable from MCC to control station next to motor
Max length of control cable from MCC to control station next to motor
(OP)
Hello,
I'm sizing the control cables that go from an MCC to the respective control stations next to each motor (Start+Stop Pushbuttons on the field)
In some cases the cables reach up to 500 meters long, and I would like to know how I can choose the right cable for each case (IEC-mm²).
In general, we are planning to use 7x2.5mm² cables as a standard in the project
In the link below, I found information about the effect of capacity on long cables, but I hope someone can give me some advice based on their experience, as we are buying a Schneider Electric Okken MCC and the interposing relays were not yet defined
Link: http://www.moeller.net/binary/ver_techpapers/ver94...
Best regards,
Juan
PS: I hope to have posted this topic in the right place, if not, please let me know
I'm sizing the control cables that go from an MCC to the respective control stations next to each motor (Start+Stop Pushbuttons on the field)
In some cases the cables reach up to 500 meters long, and I would like to know how I can choose the right cable for each case (IEC-mm²).
In general, we are planning to use 7x2.5mm² cables as a standard in the project
In the link below, I found information about the effect of capacity on long cables, but I hope someone can give me some advice based on their experience, as we are buying a Schneider Electric Okken MCC and the interposing relays were not yet defined
Link: http://www.moeller.net/binary/ver_techpapers/ver94...
Best regards,
Juan
PS: I hope to have posted this topic in the right place, if not, please let me know





RE: Max length of control cable from MCC to control station next to motor
If you use DC control then you can go a long way at 120V DC, and a lot further at 240V DC, but DC is hard on your switching devices.
RE: Max length of control cable from MCC to control station next to motor
Luckily, we are using 110 Vac as our control voltage
If you find that spreadsheet, I would appreciate it if you can share it
I was researching with our vendor and he gave me some tables of their own, but I would like to have a more generic calculation, in case the same situation happens in the future with other equipment
Sincerely,
Juan
RE: Max length of control cable from MCC to control station next to motor
The results seem to be fairly conservative - we had no problems in the installation we designed using this spreadsheet.
RE: Max length of control cable from MCC to control station next to motor
I wasn't considering the disconnection time as a limitation in cable length
You have downloaded it from the internet or created it yourself? If possible I would like to unlock the spreadsheet to follow the calculation procedure
PS: What is ICI? Those acronyms are not known in my country (Argentina)
Regards,
Juan
RE: Max length of control cable from MCC to control station next to motor
Keith Cress
kcress - http://www.flaminsystems.com
RE: Max length of control cable from MCC to control station next to motor
ICI was Imperial Chemical Industries, a huge chemical conglomerate in the UK. The company was broken up during the late 1980's and 1990's, with the loss of many jobs and to the detriment of the UK's chemical industry. https://en.wikipedia.org/wiki/Imperial_Chemical_In...
Keith - thanks.
RE: Max length of control cable from MCC to control station next to motor
Scotty, thanks again!
RE: Max length of control cable from MCC to control station next to motor
With AC control and long-lines; the other issue that is good to avoid is the sealing in (ie holding-in) of a coil. This is a result of leakage current caused by the line-to-line capacitance between parallel conductors within the same cable assembly.
As Scotty pointed out the best way to avoid this is to use DC voltage and interposing control relays. I would think that you could make it work with 24Vdc (even at 500m).
GG
"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)
RE: Max length of control cable from MCC to control station next to motor
Thanks for your contribution
Actually i can not imagine a control circuit in which I do not keep a contactor coil o auxiliary relay coil sealed during the motor operation
I understand that the use of an auxiliary relay still has the problem of the cable capacitance, am i right?
PS: I have not made any calculations yet but I think that with 24vdc the command cables must be quite oversized so as not to have a high voltage drop
RE: Max length of control cable from MCC to control station next to motor
Yes the issue with leakage-current, caused by the system capacitance, is actually worse with small AC relays, than (say) as compared to
trying to dropout the contactor without a relay.
I think you should consider doing the calc with 24Vdc and 500m; it might work with standard conductor sizes. I have seen this kind of distance done before, at 24Vdc, with #14awg conductor size. Obviously you want to select a relatively sensitive relay.
GG
"I have not failed. I've just found 10,000 ways that won't work." Thomas Alva Edison (1847-1931)
RE: Max length of control cable from MCC to control station next to motor
RE: Max length of control cable from MCC to control station next to motor
Our control voltage is already chosen (120 VCA) but i'll keep in mind your advices for a future
Thank you!