contact resistance 3

[Martintin]

Hi,

I have installed some electrical equipments in a vehicle and i have to measure the contact resistance for every grounding (equipment to chassis) that i've made.

My question is: Do you know what is the electrical standard (MIL) that specifies what is the right value for the contact resistance?

Thank you!

Martin

 

[VEBill]

"The nice thing about standards is that there's so many from which to choose."

You're best bet is to go back and check the formal requirements for your project.

The lowest standard that I recall seeing is 2.5 milliohms.

 

[Martintin]

Thank You very much for your answer.

My problem is that the customer doesn't have any kind of formal requirements for this issue.

I found in MIL-STD-202G Method 307 the right procedure, but i didn't manage to find the maximmum value for it.

The measurements i've done were lower than 2.5 mO - so that's a relief.

Martin

 

[OperaHouse]

Just a comment for those who haven't ventured into micro resistance, it doesn't have to be expensive. I bought a $4 50 watt torroid power transformer and only used the primary for power. Wound 6-8 turns of #12 wire on it for the high current. This can give me up to 30A for testing at low voltage. A current clamp and a good millivolt range meter is all you need. Very interesting what you find sometimes.

 

[itsmoked]

Nice idea Opera.

 

[zeusfaber]

Can't lay hand to the US requirements, but if you were putting communications equipment onto a UK military vehicle (and I don't see the technologies or susceptibilities being all that different), you'd probably be asked to work to DEF STAN 58-6

http://www.dstan.mod.uk/data/58/006/00000100.pdf

This tends to ask for bonding resistances not to exceed 2 milliohms.

DEF STAN 59-41 Pt 6 offers useful guidance on why this sort of bonding is important, and how it might be achieved.

http://www.dstan.mod.uk/data/59/041/06000100.pdf

A.

 

[Martintin]

Thank you for your response.

I manage to find the proper standard for grounding, bounding and shielding: MIL-STD-1857 (HDBK from 1998).

The contact resistance is 2.5 milliohms.

Thank You!

 

[ScottyUK]

Operahouse,

Similar idea to yours - use a current transformer and energise the primary from a variac. Obviously it helps to have some idea of the kneepoint voltage - a Class X CT from a high-Z relay scheme is ideal for making a controllable high (kA-level) current source.



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