Help with drawing ladder/wiring diagrams?

Thread Starter

muffintop

Joined Jun 9, 2018
4
Hey guys I am an apprentice electrician and we are working on motor control diagrams. I am having trouble understanding where to even start. We go to school for a week then work in the field for 6 weeks, then back to school. It's hard for me to understand this stuff and try to teach myself about it, I learn by seeing things done or being explained. Anyways I have to draw up 10 ladder diagrams by next week and I am struggling, here are the assignments: https://imgur.com/a/dFgsmYz If anyone could offer my any advice, resources, or just an example it would really help me out. Not being able to ask questions or see it done in class is killing me. Thanks in advance for any help, I'd really appreciate it.
 

Thread Starter

muffintop

Joined Jun 9, 2018
4
Thanks Max! I am in North America so we use the NEC.

Just figuring out how to order all the devices to make the circuit function correctly. Plus it seems odd that one rail would be the hot and the other would be the neutral, when you wire it up it seems like you'd need more than just an in and an out on the hot. I've been watching some youtube videos by Pete Vree that seem to help out with general understanding but then I look at my assignment and it's hard to understand the order and if they need to be series or parallel and how things relate from rung to rung. I'm probably just over thinking it at this point!
 

MaxHeadRoom

Joined Jul 18, 2013
22,823
Plus it seems odd that one rail would be the hot and the other would be the neutral, when you wire it up it seems like you'd need more than just an in and an out on the hot.
Not sure of what you mean here?
Incidentally in drawings such as I referenced, and older ones, you will probably come across where the O/L's of a motor etc are shown between the contactor coil and Neutral.
This now considered bad practice and should be in the main string on the left of the contactor coil.
It would also help to obtain a copy of NFPA79, there should be a copy out there in pdf.
Max.
 

Thread Starter

muffintop

Joined Jun 9, 2018
4


Does this look like it would work for #1? Single pole toggle switch, single start/stop button, pilot light to indicate motor is energized, overload protection.
 

MaxHeadRoom

Joined Jul 18, 2013
22,823
That looks OK, except for the position of the O/L contact, should be on the other side of the coil.
Also the holding contact should have the same notation as the relay it is on, in this case M.

There is no positive evidence of why the O/L were done this way, one explanation is back when start/stop stations where implemented in one unit it was convenient to wire it up this way.
But now considered a safety risk.
Max.
 
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Thread Starter

muffintop

Joined Jun 9, 2018
4
Thanks Max, so when you land on a real coil does that include the overload protection then? Is it just shown in the drawing to symbolize that it is there? We are going to be wiring these up in class so I'd like to know if there are two separate locations on the starter or just one.
 

MaxHeadRoom

Joined Jul 18, 2013
22,823
The M could be the contactor coil itself, the O/L is usually an add on or attachment to the output side of the contactor and has at least one N.C. contact for detection purposes, in some cases a N.O. also.
95 96 terminals is the O/L N.C. detect contact.
Max.

upload_2018-6-12_22-10-33.jpeg
 

MaxHeadRoom

Joined Jul 18, 2013
22,823
Incidentally if you are wiring a 1ph motor using a 3ph contactor and O/L it is normally done this way.
See p79-59 of pdf for schematic layout.
Max.

 

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