Proper order of overloads and contactors 1

[eeprom]

Hello,
On most drawings I see of motor wiring, the breaker is shown first, followed by the contactor, then followed by the OL. With MSPs, this order isn't possible anymore, as the breaker and OL are one single device. But people still draw that way, and even Autocad's electrical symbol library show that breaker, contactor, OL order. Is there now, or was there ever, a benefit to putting the overload downstream of the contactor? FYI, I'm referring to small motor applications where the OL actually breaks the current and the control circuit.

thanks
EE

 

[jraef]

Going out on a limb here to assume you are referring to North American symbols, IEC sysmbols are different and don't really have this problem.

No, it makes no difference. It was only ever done on motor starters for the sake of convenience because early overloads were dash-pot oil delayed current sensing relays and if the oil leaked, it would be really messy and potentially dangerous to have them dripping oil onto the contactors. So the dash-pot oil relays were always at the bottom of the panel and that's where you would terminate the motor leads. Design followed convention and eventually it just became the standard symbolic representation.

By the way, if you look at it, the drawing symbol for a Thermal Magnetic Circuit Breaker is going to show the same component elements as a Motor Protective Switch, so I use those. I've seen some people put a slanted arrow through the thermal symbol, I assume to denote adjustability, but that is not a standard ANSI symbol. I just put a small label next to it that says "Motor Protective Switch with TOL", no big deal.

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[eeprom]

Jraef,
Thank you for that highly informative answer. I knew there was a reason.

EE