Can changing wire gauge affect EMI certification

[Brendan Simon]

Hi EMI friends,

I have a system that has equipment enclosed in a steel box, including a PLC that operates some valves. The wires to the valves are twin core 18 AWG, but I have a some 20 AWG that I would like to use.

Does anyone know if using the 20 AWG wire (instead of 18 AWG) would significantly affect EMI such that the system would need recertification ? I'm assuming not, since it's totally enclosed in a steel box, but EMI is crazy stuff, right

According to wikipedia, the resistance of 20 AWG is 33.3 milliohm per metre, and 18 AWG is 21 milliohm per meter. The absolute numbers are quite small but the relative difference is quite significant -- an extra 50%.

Increasing the resistance of a wire increases the antenna affect. The valves have a rating of 8VA and operate at 24V. The inrush rating is 30VA. So I'm guessing the current is approx 300mA (or 1.25A inrush). Are these values significant enough to cause significant antenna radiation ? Wire length is approx 1 metre.

Thanks for any info.
Brendan.

 

[Minder]

In NA the ampacity of 20awg is 5amps, I am assuming they are AC solenoids, so Important to use twisted conductors. Also proper grounding and bonding.
Is there particular EMI regulations in Oz?
I prefer using DC solenoids where possible due to the lower problems and longevity.
M.

 

[AnalogKid]

Certs requirements vary significantly among countries. For US military projects, changing the wire gague would require a recert. Changing the manufacturer to an identical wire with a different UL registration file number would require at least an audit.

ak

 

[Arouse1973]

AKs right. Depending on the directive your testing to will depend whether a re-test is needed. If it's Radio, military, automotive then yes. If it's generic like 2004/104 which replaced 89/336 here in the UK then due diligence would require at least another DOC or an emission / immunity sweep. This can be done at a non qualified test house and the results put into a report. This just covers your back and shows you have done what you felt was right for the change you did. I personally don't think it will make any difference at all.
Adam

 

[Brendan Simon]

Thanks for your replies

I'm fairly sure the valves are DC (not AC) as only a 24VDC signal is applied to turn them "on" or "off". I think they are Burkert 0330 valves.

Existing certs are for FCC blah blah blah (Class A) and EN 61326-1, and the application is for industrial use, test and measurement. I've advised the owner of the system to document the proposed changes and consult with a local EMC/EMI test house or consultant to get some feedback on what the minimal process would be. e.g. simple document audit, minimal quick and dirty EMI sweep of system (before and after), or more rigorous testing. I guess it comes down to cost and the amount of work involved as to whether the change is worth while.

Thanks for all your help.

 

[Minder]

If you want to protect the PLC outputs, ensure you place a BEMF diode across the coils if DC.
M.