Is there any book or site where I can read more up on this?It depends on how long is the extention cable.
If the 10 Amps extention is 20 times longer, then value could be acceptable; If the two extention cables have the same lenght then the 10 Amps one must be checked because resistance is too high.
Check for loose screws ; oxidated or burned temination.
If you don't find the reason for such a high resistence than discard the extention because could be dangerous.
Alberto.
I think the OP is meaning to check the resistance of each conductor, not polarity, since AC power presents an alternating polarity between phase to phase and phase to neutral.hi all,
I know how to check the polarity of a single phase extension cable. I have never checked the polarity of a three phase extension cable.
This is not accurate . In 3 phase wye systems it may or may not carry a neutral, that is you will get phase voltage --line to neutral and line voltage --line to line . line voltage is 1.732 * phase voltage.AC has not a polarity actually. Maybe you mean to distinguish between the live and the neutral wires. In a three phase system you have only three phases (live wires) and not neutral.
Swap any two HOT lines (L1, L2, or L3). Leave ground and neutral (if any) where they are. I know it's obvious, but I have seen people do it wrong...If a motor runs backwards, reverse ANY two lines.
line voltage is 1.732 * phase voltage.
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