Newbie Industrial Electrician 1

[gilldawg79]

Looking for the answer to 3 questions. I am a new hire at a paper mill as an electrician with no industrial experience. I have a degree in industrial technology and had some motor control classes about 12 years ago, but I am rusty....I can read prints and wire up simple stop start circuits with several hardwired interlocks in them without prints, but I got asked a few questions today that I need to know the answer to.

If for example I have a Size 1 contactor, How do I know what size control circuit transformer do I use and how to fuse it on both sides (Primary side 480VAC and Secondary side 120 VAC)?


CT's what does it stand for and are we talking about the same thing even on solid state overloads on a starter?


How do thermal overloads work??? I know that a motor can trip out and that it breaks the neutral on the control circuit, but it doesn't do anything on the heater coils on the 480 side of the contactor. How is the neutral broke? is there another set of contacts at the bottom of the starter where the neutrals are and does it work by heat heating up some kind of metal that "opens" the contacts of the neutral?

thanks for the help!!

gilldawg79

 

[BJC]

You need to spend some money on Books. N0 1. American Electricans Handbook.
Look on eBay and used bookstores for the old Westinghouse Maintenance books. There are several editions.
Read catalogs, some are better than others.

 

[itsmoked]

If for example I have a Size 1 contactor, How do I know what size control circuit transformer do I use and how to fuse it on both sides (Primary side 480VAC and Secondary side 120 VAC)?

You need to look up what the coil for the associated contactor needs. Then give a little room for other associated loads. Add them all up.

CT's what does it stand for and are we talking about the same thing even on solid state overloads on a starter?

Current Transformer. Yes same thing a non contact way to measure the current in large/higher voltage circuits. Never open circuit them as some can develop fatal voltages.

How do thermal overloads work??? I know that a motor can trip out and that it breaks the neutral on the control circuit, but it doesn't do anything on the heater coils on the 480 side of the contactor. How is the neutral broke? is there another set of contacts at the bottom of the starter where the neutrals are and does it work by heat heating up some kind of metal that "opens" the contacts of the neutral?

The overloads work by being a bunch of series contacts that are in line with the contactor coil. They are resistively heated and if the motor load grows too great they will (bi-metal) open dropping out the motor contactor.

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[waross]

itsmoked summed it up well.
All starters are not created equal so you have to check the manufactureres literature to determine the draw of the operating coil. This information can usually be found in the catalog In some catalogs it is listed in the repair parts section rather than in the contactor section.

Overload relays have one or more contacts that are wired in the grounded circuit conductor of the coil circuit. Technically there is no neutral in a two wire circuit.
Some circuits use line voltage for the coil and so the line in which the overload contacts are wired is neither a neutral nor a grounded circuit conductor.
The contactors are wired this way to minimize the possibility that they will be inadvertently bypassed by someone wiring in interlocks.

When you mention heaters, the heaters typically cause a bi-metal strip to bend in response to load current. If the current exceeds the set point the bi-metal strips will bend far enough to open the contacts.
An exception is a design that uses a melting alloy and a ratchet to hold the contacts closed. Excess current through the heater causes the alloy to melt and release the shaft with the ratchet. The ratchet turns and releases the contacts. These must be reset manually. If an impatient operator tries repeatedly to reset too soon, a "cold solder" joint will develop. The unit will then lose calibration and repeatedly operate at less than rated current. This can also destroy the heater-ratchet unit by pumping the alloy out of the mechanism.
The cold solder issue may be repaired by heating the unit above the melting point of the alloy and allowing it to cool slowly, if the alloy has not been lost.
In regards to CTs, a motor drawing 180 amps may be protected by heaters rated at 180 amps, or it may be protected by a combination of 200:5 CTs and an overload relay with heaters rated at 4.5 amps.
respectfully

 

[advidana]

see if one of your teachers from your old trade school is still around that can explain starters for you.

Ask any of the electricians working with you for some help.

Go to the EC&M website and ask these same questions. Also that web site has books for sale that can explain starters for you.

Get yourself a Square D Catalog and other manufacture catalogs such as General Electric and Cuttler Hammer etc. They have a lot of tables in the back pages and in the techical sections of the catalogs with useful informaton and tables for sizing starters, control tranformers and wiring diagrams for starters.

call the sales representative on the brand of stater you are working on find out the recommend fuse sizes for you starter.

good luck.

 

[Zogzog]

Take a good industrtial electricity course.

 

[Gianoli]

" Control of Electric Machines by Irving L. Kosow " is one of the better books I have read on motor control.

Eutectic alloy or bimetallic motor overload relay are popular for smaller motors however, solid state relays are also available and becoming more common with new installations.

 

[oldfieldguy]

Be very, very careful...

I concur with Zogzog: Try to find and industrial electrical course where knowledgeable people guide you through some of the hands-on parts of your new field.

Sometimes these people are your co-workers. Sometimes not. Several times in my career I have been amazed at what has been related to me as "fact" by "experienced and knowledgeable" plant electrical workers.

Electricity is very unforgiving,and in the industrial world, there are quite a few things that are not readily apparent that can seriously affect reliability, and even worse, can be fatal.

Failing that, good luck!

old field guy

 

[ruggedscot]

A new hire at a paper mill with no industrial experiance, Hmmm you really really need to think this one through - some of the questions you asked have me worried, if you are going to be working front line you really need to be sure of what you are doing and how you are going to do it, going by the seat of your pants in a position like this is a worry, you are doing a job that your experiance is letting you down, This has an effect of putting you at risk and those that work around you.

Get some training and get some really good books on industrial electrical works.

Rugged

 

[gilldawg79]

ruggedscot,

I probably won't be turned loose for a year. For the next year I will be with an experienced mechanic to work on this stuff. These questions arose from a particular segment of training that I was going through. By no means am I walking through the gates and going to work on my own. These questions were just to solidify what I thought I knew. I knew I could get a technical answer here rather than a " when the motor pulls too many amps the overloads trip out". I understand electricity and the effects it can have on myself and others. I came from a commercial/residential background and just haven't seen this stuff since trade school. I am just a little rusty. However, I understand where you are coming from. We have to go through 2.5 years of training before we are effectively "turned loose", so I have plenty of time to ask questions, and am encouraged to do so.

Thanks,

Jimmy

 

[cuky2000]

I am wondering if there is any risk of noncompliance with the provision on the NEC, NESC, and OSHA regarding qualified and trained personnel.

If I will work in this plant, I will not be filling comfortable having an unqualified plant electrician for several reasons:

1) Personnel Safety.
2) Potential production loss
3) Equipment damage.

I suggest considering taking seriously the safety part and avoid any unnecessary risk for yourself and others. Made sure you work closely to an experience plant electrician and obtain an accelerated training ASAP.

Check if the enclose link could help:

http://ecmweb.com/ops_maintenance/electric_case_surface_miner/

http://onlineoshatraining.homestead.com/index.html?gclid=CInQy7Gn94wCFSe9Igod8w-EAw

http://www.lbl.gov/ehs/pub3000/CH08.html

 

[ruggedscot]

If you have 2.5 years to go before being let loose then this is different to the impression that you gave before << a new hire at a paper mill >>


I didnt realise that you were being trained, is this a proper training course and one that you will recieve the right training for the job in a format that is official ?

If not then I think that you need to be sure on this one.

Id have concerns on the following :- How did you get the job,
a) did you give an impression that you were better qualified than what you are?
b) is the outfit professional?
c) is it a means to get someone for less money ?

Id be hell of a concerned if you gave an impression that you were more skilled than what you were, mainly because of the risk to yourself and others. Paper mills are not the place for inexperiance or gungho attitudes.

If they are employing you to save money then that again would be a concern,

Rugged