# Why is it bad to run power through BNC (RG58) cables?

A standard practice in many academic labs, which I'm told is "bad practice", is to use RG58 cables (i.e. standard BNC cables) for power distribution.

Question 1: Why is this considered bad practice?

Question 2: Is there a different sort of cable which is better for power distribution and compatible with BNC connectors?

• 3v, 5v, 12v or 240v? – Solar Mike Oct 29 '19 at 20:52
• @SolarMike 24 V. – Yly Oct 30 '19 at 7:01
• @Yly how much of current. AC or DC power. – user1586 Oct 31 '19 at 17:22

Because it is not a power cable (Q1) using power connectors (Q2).

BNC cable has a solid conductor and a ground braid to electrically shield and mechanically protect the conductor.

Electrical reason: Some ground braids are made of steel, which is not as good a conductor as copper, so voltage losses to the wire would be higher than copper wire. Basically, wasted power.

Edit....

Current creates heat ($$I^2 R$$ losses). The ampacity rating of a power cable is determined by the maximum temperature the cable's insulation can handle. The BNC wire was never meant to carry power, so the current flowing may cause the insulation to break down and cause a fire.

Safety reason: The main reason BNC cable should not be used to send power is because of the connectors. The outside of the metal BNC connector is uninsulated, so you have a shock risk, if you disconnect the load terminal while power is being applied.

Common sense reason: You may know what you have done so are not at risk, but an unsuspecting person is NOT expecting power on a signal cable.

Even if you found an insulated BNC connector and added a warning sign, if it was disconnected a user may connect a normal connector negating your bad practice.

No one expects power over a BNC cable. So power distribution over BNC cables is bad practice.

Cost analysis $$BNC= C_i + C_d + C_c + C_s$$ $$PowerCable(1 core) = C_i + C_c$$ $$C_i$$ = cost of insulation; $$C_d$$ = cost of dielectric; $$C_c$$ = cost of core; $$C_s$$ = cost of sheilding; Clearly power cable is cheaper.

Utility analysis

• BNC: used for signals, interference is enemy.

• Power Cables: used for voltage transmission, interference does not matter too much cuz power is transmitted at 50 or 60 Hz and noise (in the environment) is high frequency (radio, broadcasts, radiations, etc.) and very low voltage almost all good electronics filter the input voltages.

Is it bad practice? only if you don't need it. and if you have to choose to buy between them. The cheapest solution is always the best. if you already have them around (and they will not fail)- go nuts.

Langmuir probe (100V DC and 150mA). use BNC cables because of they need very precise measurements.

options are power connectors, wire harnesses, etc.

PS

1. Dielectrics come in all shapes and sizes is a special kind of insulator(simply put).
2. there are copper BNC cables, and BNC doesn't waste power (They are for signals).
3. Idiots should not be allowed near power electronics. Don't touch the connector body of BNC. it is usually grounded but not in research areas.
4. Science is not common sense. Common sense varies with region and knowledge. it is based on proof and observations and everything has a definite reason.