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about insulation requirements for 220v

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csdave

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Hi all,
this may seem basic and stupid, but I really haven't found a precise reference on this and posting here is easier than searching more ;)
How far apart should 220v wires be on a circuit?
Is there any danger of an arc being created? At what distance?

Say I have two exposed wires and want to prevent them from causing problem if they accidentally touch. Is wrapping them inside insulating tape enough? (not that I work with exposed wires, but it's just to understand what the amount of required insulation is.

Thanks ;)
 

phobika

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basically a 220v supply line can't create a sustainable arc in open air conditions because air is a very good dielectric if you really want to know the minimal distance we need to get back to the coulombs law & you may get a very small distance,now if in case they did form a arc they can't be sustained because the wires get hot & they meltdown, cutting a power, this's in case of a domestic supply line..but by using a stepdown transformer & by obtaining high current & low voltage,we can create a arc.this's the technique used in "arc welding".
hope this cleared the doubt.
regards.

---------- Post added at 17:39 ---------- Previous post was at 17:35 ----------

Hi all,
Say I have two exposed wires and want to prevent them from causing problem if they accidentally touch. Is wrapping them inside insulating tape enough? (not that I work with exposed wires, but it's just to understand what the amount of required insulation is.

Thanks ;)
yeah,if wrapped properly they are more than enough.
 

csdave

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basically a 220v supply line can't create a sustainable arc in open air conditions because air is a very good dielectric if you really want to know the minimal distance we need to get back to the coulombs law & you may get a very small distance,now if in case they did form a arc they can't be sustained because the wires get hot & they meltdown, cutting a power, this's in case of a domestic supply line..but by using a stepdown transformer & by obtaining high current & low voltage,we can create a arc.this's the technique used in "arc welding".
hope this cleared the doubt.
regards.

---------- Post added at 17:39 ---------- Previous post was at 17:35 ----------


yeah,if wrapped properly they are more than enough.
Thanks,
that's as I remembered from studying arcs some 20years back but I needed to be sure ;).
 

FvM

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I suggest, not to rely on the assumption of "can't create a sustainable arc in open air conditions". It's unfounded. But I also think, the "sustainable" point is not actually related to your original question.

When designing insulation, you have air gap, creepage distance and insulation layer thickness. Both air gap and insulation layer calculations are based on dielectric strength data. But they also have to consider field strength variations due to the conductor radius and inhomogeneity of an insulator material. Finally partial discharge phenomena with AC voltages play a role. And there's a safety margin applied. As a result, the insulation thickness of a cable rated for 230 V will be a multiple of the amount calculated according to dielectric strength. "wrapping them inside insulating tape" can be accepted as a suffcient insulation under some restrictions only, but works, of course.
 

phobika

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the assumption of "can't create a sustainable arc in open air conditions". It's unfounded.
i too accept it's unfounded, but for a domestic 220v supply, for normal wires it just can't hold the intensity of a arc.
but for proper insulation i accept what you have stated above.:grin:
 

FvM

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for normal wires it just can't hold the intensity of a arc.
"can't hold" still sounds misleading to me.

You started however with a consideration about good dielectric properties of air. As we all know, the dielectric properties don't describe the plasma state of matter. "Wires get hot & they meltdown" is in fact the most plausible point. But how long an arc will be sustained? This wasn't the OP's question, but is interesting anyway. In most cases, the circuit breakers will stop it, so you don't have a chance to see the wires melting. But depending on the wire shape and current limiting impedances, an arc may burn quite a long time, sufficient to burn down a house at worst case. An even more serious problem with "sustained arcs" exists in power distribution systems. Most of the officially required protection equipment for electrical workers is considering this dangerous situation.
 

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