Using Magnetic Contactors in Residential Application

MaxHeadRoom

Joined Jul 18, 2013
22,845
As far as control (stranded) voltage conductors TEW/MTW etc it is rated at 600v.
If the control voltage is 230v, I use TR64 control wire, it is rated for 300v. and has a very much smaller diameter making it ideal for Duct wiring, or confined spaces.
Max..
 

MisterBill2

Joined Jan 23, 2018
8,443
Makes sense. It's just one of those oddities. Scientifically, I'd figure peak voltage.

So 300/1.4=214 which is 168 V 0-peak+(margin of safety). You would generally use 300 V rated wire for 120 VAC.

Finally: https://sielearning.tafensw.edu.au/toolboxes/Electrotechnology/toolbox/hq/mag1/ratings.htm#voltage



This is the first time I saw a reference to RMS.

Even this https://en.wikipedia.org/wiki/Electrical_breakdown isn't good, although there is a VI relationship.

Dielectric strength https://en.wikipedia.org/wiki/Electrical_breakdown is typically in V/m, so it's like confusing.

So just like a 3/4 fitting inplumbing is a 7/8 fitting in HVAC and all optical (eyeglass) screws (purchased from an optical supplier) are specified in Overall length no matter the head type.

So when you take: 300 V hookup wire: https://www.awcwire.com/productspec.aspx?id=ul-1569-hook-up-wire
  • Insulation: Polyvinylchloride (PVC), 0.016" nominal insulation thickness
Temperature Range: -40°C to +105°C (-40°C cold bend test)
  • Voltage Rating: 300 volts

and apply the PVC values from here: https://omnexus.specialchem.com/polymer-properties/properties/dielectric-strength of 10-30 kV/mm things still don;t work out.

0.016" = 0.4 mm.; 0.4 * 10 kV; 0.4 * 10 = 4 kV?

So, something else is going on.

Another search that was hard to find (nearly impossible) is the differences between tape out and line in levels for consumer equipment.
Back a long time ago, 1975 or so, "tape out" was used to avoid needing to be close to what was "Line Out" which was supposed to be 0 VU, about 0.707 volts in a 600 ohm system. Then somebody decided that making it louder, (Higher voltage) would be more impressive and presumed to be better quality by the folks who equate louder with better. Fortunately the broadcast industry folks did not follow. So today "Tape Out" may vary from a half a volt to several volts, at any random source impedance.
For the sizes in plumbing and air conditioning, plumbing references Pipe sizes based on inside diameters because pipes are selected for flow rates, while Air Conditioning and refrigeration are using TUBE sizes because tubing goes into fittings often brazed or welded or silver soldered.
 
For the sizes in plumbing and air conditioning, plumbing references Pipe sizes based on inside diameters because pipes are selected for flow rates, while Air Conditioning and refrigeration are using TUBE sizes because tubing goes into fittings often brazed or welded or silver soldered.
Yep. It's just that I like long sweep elbows when installing a water heater. I am EPA certified for amall appliance and automotive AC. That was an easy test. I had a course in fluid mechanics.

machinist: I was mentored by a real machinist at work and I had 24/7/365 day machine shop access. Although I had a mig, tig and stick welder in my hands at least once and I did exceptionally well, the director said NO to the welder for all but 1 person. I would not be able to set up a weld. Same way I learned the mill. Set-ups were verified before I could proceed.

I was the best person that could silver solder. Soldering and welding came from lots of soldering experience with wierd alloys including indium and plumbing. I'm also sure glass blowing (mainly sealing quartz tubes under vacuum) had a lot to do with it.
Anytime there was a significant gap in not doing glass blowing, I had to practice at least once.

The eyeglass screw thing was wierd. if the screws are ordered from a non-optical company then they are what i call "NORMAL".

Then there is a Yard of concrete. It's a cubic yard.
 

MisterBill2

Joined Jan 23, 2018
8,443
Yep. It's just that I like long sweep elbows when installing a water heater. I am EPA certified for amall appliance and automotive AC. That was an easy test. I had a course in fluid mechanics.

machinist: I was mentored by a real machinist at work and I had 24/7/365 day machine shop access. Although I had a mig, tig and stick welder in my hands at least once and I did exceptionally well, the director said NO to the welder for all but 1 person. I would not be able to set up a weld. Same way I learned the mill. Set-ups were verified before I could proceed.

I was the best person that could silver solder. Soldering and welding came from lots of soldering experience with wierd alloys including indium and plumbing. I'm also sure glass blowing (mainly sealing quartz tubes under vacuum) had a lot to do with it.
Anytime there was a significant gap in not doing glass blowing, I had to practice at least once.

The eyeglass screw thing was wierd. if the screws are ordered from a non-optical company then they are what i call "NORMAL".

Then there is a Yard of concrete. It's a cubic yard.
I learned the mill and the lathe by fixing shop radios for all of the machinists, and mentioning one time that it would not take me any longer to learn their job than it would take them to learn mine. And knowing how to machine helped me to produce better drawings much less subject to errors, and not needing any machinist math work. THAT improved the profit on my jobs because of reducing errors and speeding the machining. Not bad for an EE, I think.
 

shortbus

Joined Sep 30, 2009
8,469
This whole wire rating thing is from mrbill making a statement something like, 120V was safer and the wire needed less insulation. So I asked him why house and industrial wire was rated at 600V. It, in my area, is printed on the sheath/insulation of the wire.
 

MisterBill2

Joined Jan 23, 2018
8,443
This whole wire rating thing is from mrbill making a statement something like, 120V was safer and the wire needed less insulation. So I asked him why house and industrial wire was rated at 600V. It, in my area, is printed on the sheath/insulation of the wire.
600 is almost as round a number as 800, but less.
 
If I understand the uk, the circuits are capable of much higher power than the US AND the plugs have fuses in them.
The US plugs definately have issues. There is no accepted right way to orient a 15 or 20A 120 V receptacle. They look like a face when the ground is pointed down. They are deemed safer when the ground is oriented up. Reason: if the plug is partially out and a sheet of metal falls against the wall it's less likely to short. I'd rater stare at a "happy face". I hate backstabbing too.

Ideal Industries had a nice product they discontinued. A Term-a-nut which was a wirenut pigtail with a wire through the normally closed side that either had a fork or pre-stripped end on it and available in white, green or black. two Hots and two N's can easily be terminated with a white and black term-a-nut pigtail and the fork terminals go to the socket. They also used stranded wire making stuffing the receptacle back in the box much easier.

Ground depends on the type of box and if the wiring was old with a ground pulled, but not a grounded receptacle installed.
insulated box, two ground to a term-a-nut pigtail, a fork terminal to the outlet. Newer Metal box: Similar, but you also need to use a ground pigtail to fork terminal. One fork to the ground on the receptacle and the other to the box ground screw.
Older metal box (Has no grounding screw). That needs a ground clip and solid wire to ground the box.

We now have GFCI's and "tamper proof" receptacles. You have to depress both Hot and N for a plug to be able to enter so it's "kid resistant". Then, of course, AFCI's and GFCI's.
 

MaxHeadRoom

Joined Jul 18, 2013
22,845
If I understand the uk, the circuits are capable of much higher power than the US AND the plugs have fuses in them.
The US plugs definately have issues.
But from my experience in the early implementation of the UK Ring Main system and the 13a outlets, the plugs had Very large brass pins compared to the N.A. almost wimpy looking comparison. And yet, the UK plugs/sockets seemed to suffer from overheating as seen by 'browning' of the plug cover.
They could not really be overloaded as the internal fuse was 13a max.
When comparing it to the N.A. version, I was surprised to see no similar event.
I assumed the problem with the 13a socket was poor contact, plug to socket.
The thing that surprised me with the N.A. version was so many appliances fitted with 2 pin plugs, and no ground pin.
e.g. Steam Irons!
Max.
 

Reloadron

Joined Jan 15, 2015
5,915
An "AC3" rated contactor means that it has three sets of contacts. So you can use one set or two sets or all three.
That's not quite what it is about. Induction Motors, all induction motors, have a starting current and we know that starting current well exceeds the run current. The starting current can run about five times or more than the run current. A three phase 230/460 VAC 5 HP motor will draw about 12.6 / 6.3 FL (Full Load) amps. Normally motor contactors are rated by the HP rating of the motor they are designed to support. What the AC3 rating is about is that the induction motor starter (contactor) is rated to handle the starting current required by the induction motor for a short (~5-7 Sec,) period of time. I only became familiar with AC1 and AC3 retings because we bought some large German machines which included several German guys to do the installation and setup. This involved Facilities Engineering which I was not but gut sucked into. I haven't a clue if there is an AC2 rating? AC1 is pretty much the same deal but a lower current rating "I think". The ratings also apply to resistive loads like heaters. and in those cases have higher current ratings since there are no peaks. That was a few years before I retired and I had never heard of that rating before.

I guess if one has enough loads to make it worthwhile 3 phase residential would be pretty nice to have.

Ron
 

shortbus

Joined Sep 30, 2009
8,469
I guess if one has enough loads to make it worthwhile 3 phase residential would be pretty nice to have.
It would be good for me, then I could get rid of the VFDs to run my machines in the barn. And many farms do have three phase and the house is off of it.
 

Reloadron

Joined Jan 15, 2015
5,915
It would be good for me, then I could get rid of the VFDs to run my machines in the barn. And many farms do have three phase and the house is off of it.
The range I shoot at is out in farm country. George Kebly started his small machine shop and was using the old Kato motor generators for his 3 phase power. There was only single phase power on that country road and when he asked the power company it was well over 100K just to bring in 3 phase. That was maybe 30 years ago. Finally came 3 phase availability maybe 5 years ago.

An old friend and hunting buddy lived on Bell Street, Webster Springs West Virginia. Bell street runs along a river at the base of a mountain. Every time there was a slide or trees washed down the mountain it took out that single wyre (I call it a wire but they call it a wyre). You not only lost power but there was then no way in or out unless you went upstream to where you could ford the river in the shallows and you needed a high 4 wheel drive. Had to love it.

Ron
 

Reloadron

Joined Jan 15, 2015
5,915
That was seriously funny. I miss my old hunting buddy. You can't start every day with a quart of Lord Calvert rot gut whiskey and live long and prosper. He was 59 when he died of alcohol. Maybe one day I'll take a ride down there and see how the few folks I got to know are doing. Nice country in the summer. :)

Ron
 

shortbus

Joined Sep 30, 2009
8,469
The old guy I used to hunt his property was named Pap Robe, my wifes uncles dad. He lived in a one room "cabin" with a potbelly stove, always had a coffee pot on top. Just dump the grounds in and add some water. The coffee was so bitter and thick from boiling the spoon would stand up in the middle of the cup.
 

PhilTilson

Joined Nov 29, 2009
93
But from my experience in the early implementation of the UK Ring Main system and the 13a outlets, the plugs had Very large brass pins compared to the N.A. almost wimpy looking comparison. And yet, the UK plugs/sockets seemed to suffer from overheating as seen by 'browning' of the plug cover.
They could not really be overloaded as the internal fuse was 13a max.
When comparing it to the N.A. version, I was surprised to see no similar event.
I assumed the problem with the 13a socket was poor contact, plug to socket.
The thing that surprised me with the N.A. version was so many appliances fitted with 2 pin plugs, and no ground pin.
e.g. Steam Irons!
Max.
I hesitate to enter this discussion, given that the topic has meandered so far from the original question! However...

Yes, the pins on British 13A plugs do seem large, but this allows much of the pin to be 'shrouded' so that it disconnects from the socket before the exposed metal part becomes accessible, thus making accidental electrocution when inserting or withdrawing plug almost impossible.
13Aplug.jpg
The usual cause of plug 'browning' is a loosening of the screw securing the Line wire to the plug pin. This creates a higher-resistance contact which gets hot and overheats the plug.

The 13A ring-main standard was developed during WWII in order to save on copper for wiring. Running a 'ring' from consumer unit, round a number of sockets and back to the consumer unit used much less cable than point-to-point wiring. It also meant that a cable of 16A capacity could supply a maximum of 32A on the 'ring', which could be tapped off at various points by various devices.

The plugs contain a cartridge fuse which means a small table lamp can be fused at 2A and allows the use of a neat, small-gauge flex, which means that if a fault develops, there is no risk of the flex catching fire by carrying the full 32A available on the ring.

Finally, just two points: to go back to the 120 vs 240 volt matter, at least the higher voltage allows the use of much smaller cables, which in turn minimises horrible messes like the picture! And three-phase domestic supplies are common in Spain, though not in the UK.Cables.jpg
 
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