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stainless steel vs bronze braided hose for a ground connection

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USAeng

USAeng

Mechanical
Jun 6, 2010
419
A few guys at our shop are going back and forth about which would be better to use as a return path to ground... about 5/8" braided either stainless or bronze about 15' long... there will be an insulated wire going through carrying the current and then it will return through the braided hose back to ground... anyone know if one will be better than the other? is there a way to measure which is better? our multimeter's lowest setting is a 200ohm scale.... do we need a better multimeter for things like this? Basically- is there something I can do to prove that one will be actually noticably better than the other? Thank you!
 
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there will be an insulated wire going through carrying the current and then it will return through the braided hose back to ground...
Click to expand...
is not allowed by NEC or any other sane code. Ground conductor shall not carry any current during normal operation. Install separate return wire in the raceway.


Rafiq Bulsara
 
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Just endorsing Rafiq's answer. Don't do it.

Good on ya,

Goober Dave
 
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Bronze has a much lower resistivity than stanless steel so in theory it would make the better conductor.

Will it make a difference in practice? That depends on the application.
 
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The braided hose has a corrigated bronze or stainless inside...would this make a difference? I definately want to inform my company of any code violations... is there a place to find this part of the code on the net so I can show them?

I think this is being planned because it seems that it is the way our competition is doing it... it is for a high energy spark rod for power plants... thanks a lot!
 
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not pressurized... I guess I would just call it braided flexible conduit for what we are using it for... but maybe using it as a path for ground is not allowed by NFPA code? Hopefully someone can clarify that... these guys here are looking to start buying and I hope I can give a good reason not to go ahead with this if there are issues with using it as a ground path... Thanks a lot
 
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What's the application? Ignitor for a burner assembly? Electrostatic precipitator? What is the voltage/frequency and ampacity? Is the "hose" carrying anything else other than the wire?

From your brief description it sounds like it is for a high voltage probe with a low current output in the milliamp range.
 
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rc - maybe an igniter for a GT or duct firing?


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Its a high energy ignitor for igniting oil... its about 2000V and I dont know how much current but its probably a few amps at least... the only thing in the hose/conduit is one hot wire... the braided hose/conduit will mate up to a spark rod that is probably about 10' long with another wire inside that matches the wire in the hose/conduit... then the current travels to the end of that, jumps the gap (sparks) and then travels back through all of that...
 
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Use something listed as an electrical conduit rather than a hose. There are flexible ones available.

Folks here are objecting to you using a grounding conductor as a neutral return, since ground is intended for faults rather than normal operation. What you are describing may be an exception, similar to an ignition system on stationary engine which uses the engine block as a return path.
 
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Bronze would probably be the best. Stainless is usually avoided for conductors.

Alternatively you might consider using copper tubing. Just run your center conductor down it.

Keith Cress
kcress -
 
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the bronze braided tube/conduit would be much nicer looking than copper tube... is there a measureable way to find out which would be a noticably better conductor?

also can anyone see any safety hazard with doing things this way... I have a gut feeling something isnt safe about it, but I am a wannabe electrical guy... this hose is out in the open where people could touch it... I suppose the current will find its way to ground, but I worry about what happens if that one connection fails and also if a person grabing the line standing on a metal platform is a better conductor than the stainless steel? I dont know...
 
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well thats what I was kind of getting at... will a resistance of 3.198 x 10^-8 for a bronze be that much better for anything here than 7.496x10-7 for a 316 stainless? I dont know what numbers for resistance that small mean... I took 1 semester of electrical engineering in school... other than that its been learning a little here and there from stuff like this website... so this is just another step on the ladder for me...

Ever since the first posts... my new biggest concern is the safety/codes...
 
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This is typical for an ignitor. The conductor connected to the the spark plug is inside a braided hose the return is the hose back to the ignitor.

The NEC does not ALWAYS apply.

I don't think it makes a significant performance difference whether it's stainless steel or bronze. They normallly are supplied with the cable. I would go with what ever the manufacturer supplied (stainless)
 
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Yes, ignitor is different and especially when it is part of a machine assembly, NEC does not apply. Safety does.

A little bit of clarification on the intended use helps a lot. I also agree that in that case bronze/brass or steel would not make much of a difference.

Rafiq Bulsara
 
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Rafiq,

The outer body of most ignitors is in intimate contact with the machine frame, and that typically has a lot of both fortuitous paths to earth and bonds to the main earthing electrodes or grid. If the braid broke I can't imagine the casing rising above earth potential. I wholeheartedly agree that a failure mode which exposes someone to igniter potential must be avoided.

Some igniter cables are basically a high temperature co-ax with a fairly heavy inner conductor - maybe 4mm2 - and a tinned or nickel-plated braided copper screen as the current return. The whole lot is then protected by a braided stainless outer jacket for meachanical strength. The cable is probably a 'special' and when we've replaced them they are insanely expensive.


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At 2000 Volts and a couple of amps, I would compare the voltage drops across both the stainless and the bronze braids.
Hint; Even at one ohm resistance the voltage drop will be 1 Volt per Amp. Then choose the material with the best mechanical specs.
Second hint; If you are going to measure the resistance directly, pass a known current through the braid and measure the voltage drop.

Bill
--------------------
"Why not the best?"
Jimmy Carter
 
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