Interlock

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kody916

Member
Location
Illinois
Hello

1. what is the definition of interlock.

2. what is the definition of electrical interlock and mechanical interlock. are they both the same?


Thanks
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Hello

1. what is the definition of interlock.

2. what is the definition of electrical interlock and mechanical interlock. are they both the same?


Thanks

1. Several dictionaries on the web.
2. Electrical interlocks are different than mechanical ones. For instance, a reversing starter has both types of interlocks that independently prevent both contractors being on at the same time.
 

JoeStillman

Senior Member
Location
West Chester, PA
Here is a 2-speed starter diagram that shows both mechanical and electrical interlocking. The mechanical interlocks are shown by a dashed line. The HI and LO contactors are mechanically interlocked - physically connected in a way that prevents them from both being in the same position. The start circuits are electrically interlocked in 2 ways; 1) aux contacts of each coil lock out the opposite coil and 2) the pushbuttons have NC contacts (another sort of mechanical interlock) that lockout the opposite coil.

Starter with SS PB-Model.jpg
 
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kody916

Member
Location
Illinois
so mechanical interlock is nothing bt mechanism that prevents two switches
to operate at the same time
and electrical interlock is when have a coil which when energised causes two or more contacts to operate
at the same time
 

Smart $

Esteemed Member
Location
Ohio
so mechanical interlock is nothing bt mechanism that prevents two switches
to operate at the same time
and electrical interlock is when have a coil which when energised causes two or more contacts to operate
at the same time
Somewhat, yes. Mechanical interlock is physical prevention of concurrent operation. It is commonly implemented by physically preventing the contacts of one of two contactors from changing to the energized state, even if the defeated contactor's coil is energized.

Electrical essentially does the same thing except usually by using an auxiliary set of Normally-Closed contacts to open the coil control circuit of the other contactor. In a sense, it is part mechanical, part electrical.
 

SG-1

Senior Member
so mechanical interlock is nothing bt mechanism that prevents two switches
to operate at the same time
and electrical interlock is when have a coil which when energised causes two or more contacts to operate
at the same time

In addition a mechanical interlock can:

Prevent you from opening an enclosure unless the handle is in the OFF position.
Prevent two breakers from being ON at the same time.

Basically, they are used make sure that physical things happen in the correct sequence to prevent human error, property damage, injury, &/or death.
 

Sahib

Senior Member
Location
India
Here is a 2-speed starter diagram that shows both mechanical and electrical interlocking. The mechanical interlocks are shown by a dashed line. The HI and LO contactors are mechanically interlocked - physically connected in a way that prevents them from both being in the same position. The start circuits are electrically interlocked in 2 ways; 1) aux contacts of each coil lock out the opposite coil and 2) the pushbuttons have NC contacts (another sort of mechanical interlock) that lockout the opposite coil.

View attachment 11489
The circuit needs a little correction: if a ground fault develops on the left side of OL NC contact, it would be bypassed.
 

Smart $

Esteemed Member
Location
Ohio
The circuit needs a little correction: if a ground fault develops on the left side of OL NC contact, it would be bypassed.
The subject has been debated here before, many times. This is how NEMA motor starters are wired from the manufacturer. They've been doing it this way since forever. Won't change just because we discuss it... :happyno:
 

hurk27

Senior Member
Another interlock that is in common use is a transfer switch, that only allows one source at a time to feed a load, it is nothing more than a multi-pole double throw switch, and is the most common method of connecting a generator to power a house or other load so that both supplies can't be tied together and on at the same time, as we know that if that happens when the utility comes back on it will destroy the generator and or can possibly cause a fire, it also prevents generator from back feeding the utility lines which could kill a lineman who is thinking that the line is not energized, it is also required by the NEC and for those who think its ok to use a widow maker cord to the dryer receptacle it can keep you from going to prison if someone was to be hurt or killed, trust me it has happened, three electrician's in Florida found out the hard way during hurricane Charley all serving 15 year sentences.

Sounds like a test question?
 
Then there is the interlock found on equipment with high (a.k.a. 'deadly') voltage inside, like a broadcast transmitter.

Usually it is a series string of micro-switches that are closed when the access panel is in place.

To prevent residual voltages from killing someone, manufacturers devised ways to immediately take the High Voltage supplies to ground when the series-string was opened.

Typically, this is a honking big solenoid which is pulled in when the series string is complete, and drops out, usually assisted by gravity, to short a pair of terminals that ground the H.V. supply.

Older equipment, however, usually employed the kind of micro-switch that was closed in two positions..one when the plunger was pushed in against a spring, and the other (when it was necessary to troubleshoot with the door or panel off) by PULLING out on the plunger.

But the advent of 'solid-state transmitters; has changed all that:

The first generation of 'solid-state' transmitters were voltage-limited to around 50-60 volts, at correspondingly high amperages to get the required power....The Harris MW-1, the first AM of that type, ran 53 volts at 23 amps for 1000 watts. Then there was a jump to about 120 volts, the Gates 'Five' series runs 106 volts @ 56 amps for 5000 watts.

Now with higher-rated solid-state devices, voltages are creeping back up, 300 volts seems to be the new 'norm'.

Scariest thing I ever saw was the meter for the High Voltage on a Harris MW-50, 50,000 watt AM...........0-30 KV.

Hope I didn't bore anyone with this.....I generally just read to pick up useful information about 'supply side of the meter' since I maintain numerous broadcast sites, from 1000 W AM's to 20 KW FM's.

Regards to all and thanks for all the education.

Gary
 
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