Uk Engineer trying to understand US system

[AdrianWint]

Hi All,

I'm an electrical engineer working in the UK for a company that makes educational teaching products. We have just begun to export equipment into the US.

The reason for this post is to ask for your assistance in verifying & extending my knowledge of the electrical system in the US.

It is my understanding that, unlike here in the UK, you have a variety of different voltage & phase configurations offered for electrical service. Perhaps the most common being the "residential" service, which is presented as a three wire service (hot, hot & neutral) with 120V between hot & neutral and 240V between hots. This is a single phase service with the two hots being opposite ends of the same winding, the neutral being the centre tap.

A more commercial service would be a 3 phase 4 wire service, consisting of three hots (phases), each 120 deg apart & a neutral. Between any Hot & neutral is 120V, between any two hots is 208V.

How am I doing so far?

Adrian

 

[ibew501ed]

right on ...continue

 

[jeremysterling]

This is a single phase service with the two hots being opposite ends of the same winding, the neutral being the centre tap.

Both of the nominal systems you describe are common offerings of our local utility, Austin Energy.

The only difference is that, here in Texas, we center-tap the winding.:grin:

 

[augie47]

The two systems you describe probably cover a large percentage of the commercial/residential services.
Add 480Y/277 (big brother to your 208Y/120) and you have covered a huge percentage of the commercial.
The remainder is a mixture of 240/480/600/2140, etc systems for industrial.

 

[ibew501ed]

The two systems you describe probably cover a large percentage of the commercial/residential services.
Add 480Y/277 (big brother to your 208Y/120) and you have covered a huge percentage of the commercial.
The remainder is a mixture of 240/480/600/2140, etc systems for industrial.

in NY we have 4160/2400 what is 2140?

 

[mpoulton]

Hi All,

I'm an electrical engineer working in the UK for a company that makes educational teaching products. We have just begun to export equipment into the US.

The reason for this post is to ask for your assistance in verifying & extending my knowledge of the electrical system in the US.

It is my understanding that, unlike here in the UK, you have a variety of different voltage & phase configurations offered for electrical service. Perhaps the most common being the "residential" service, which is presented as a three wire service (hot, hot & neutral) with 120V between hot & neutral and 240V between hots. This is a single phase service with the two hots being opposite ends of the same winding, the neutral being the centre tap.

A more commercial service would be a 3 phase 4 wire service, consisting of three hots (phases), each 120 deg apart & a neutral. Between any Hot & neutral is 120V, between any two hots is 208V.

How am I doing so far?

Adrian

Yes. In ANY building in the US, normal receptacles are 120V single phase, on 15 or 20A circuits. Buildings fed with higher voltages use transformers to provide 120V power for receptacles. Higher voltages or more phases are only used for high-power equipment or commercial lighting. If the equipment you are producing uses less than 1800 watts or so, Americans would expect it to operate on 120V. The next step up from that would be 208-240V single phase. Residential and small commercial services will provide 240 (single phase), while larger commercial services will give 208V (two phases of 120/208Y). Being able to use either voltage would be great, and most equipment can. Above about 10kW, it would be normal to expect equipment to use 480V 3 phase.

 

[AdrianWint]

Thanks for the replies Gentlemen.

It's good to hear that I've at least got a basic grasp of the US system!

Round 2 - a little more detail.......

From mpoulton's post above, the suggestion is that any device upto around 1800W should be designed to be fed with a 120V supply. I guess this would be via a flexible power cord terminated in a NEMA 5-15 (??) plug with the internal cores coloured black (hot), white (neutral) & green (ground). Is this correct / what you would expect?

Lets consider something a little bigger..... one of our products has a 2000W water heater inside it. This heater expects 230V ( + or - 10%), so would be OK on both 208 & 240V (lets ignore the fact that it will disipate a different power for the moment). And lets assume, for the moment, that the equipment does not require a neutral...... only 2 hots & ground. Should it come fitted with a NEMA 6-15 plug or with bare wire ends? What colours would you expect the cores of the cord to be? What about the same product, but now it does require the neutral. Should the plug be a NEMA 18-20? What do the markings X, Y, W & Z in drawing of the connector mean..... I guess the 3 phases plus neutral..... but Im not sure which is which!


Thanks again for taking the time to educate me!

Adrian

 

[whillis]

From mpoulton's post above, the suggestion is that any device upto around 1800W should be designed to be fed with a 120V supply. I guess this would be via a flexible power cord terminated in a NEMA 5-15 (??) plug with the internal cores coloured black (hot), white (neutral) & green (ground). Is this correct / what you would expect?

You are correct, a 5-15 plug would be acceptable. The colors are normally white (neutral), black (hot), and green (ground) but blue (neutral), brown (hot), and green (ground) should also pass.

Lets consider something a little bigger..... one of our products has a 2000W water heater inside it. This heater expects 230V ( + or - 10%), so would be OK on both 208 & 240V (lets ignore the fact that it will disipate a different power for the moment). And lets assume, for the moment, that the equipment does not require a neutral...... only 2 hots & ground. Should it come fitted with a NEMA 6-15 plug or with bare wire ends? What colours would you expect the cores of the cord to be?

Is this a fixed device or is it portable? If it's fixed I would expect something like this to come with a junction box where I could connect my own wiring appropriate to the installed location.
If it's a portable device then a 6-15 plug would be acceptable. Wire colors should be black, black, and green or black, red, and green.

What about the same product, but now it does require the neutral. Should the plug be a NEMA 18-20?

No, a 14-15 plug would be more appropriate.

What do the markings X, Y, W & Z in drawing of the connector mean..... I guess the 3 phases plus neutral..... but Im not sure which is which!

X= phase A (usually red), Y= phase B (usually black), Z= phase C (usually blue), W= neutral (white)

 

[shuntripper]

W/H comes with a pigtail?

W/H comes with a pigtail?

any water heater I've ever seen came with an integral J box and a KO. It's not a motor so it doesn't require a disconnecting means. Most efficient just run a piece of flex to the WH.

 

[Smart $]

...

Lets consider something a little bigger..... one of our products has a 2000W water heater inside it. This heater expects 230V ( + or - 10%), so would be OK on both 208 & 240V (lets ignore the fact that it will disipate a different power for the moment). And lets assume, for the moment, that the equipment does not require a neutral...... only 2 hots & ground. Should it come fitted with a NEMA 6-15 plug or with bare wire ends?

While I agree with whillis that a 6-15 plug would be acceptable, don't get the impression it is the most-commonly-used plug/receptacle configuration for 208/240. IMO, an L6-15 is more commonly used (but I have more of an industrial background in these regards). There is no standard or most-commonly-used configuration AFAIK. Any 250V — 2-POLE, 3-WIRE GROUNDING configuration will work, so it's simply a matter of matching the plug and receptacle. In most cases, the receptacle would be installed as a dedicated circuit for such a piece of utilization equipment. Without knowing the likely uses of your product, I'd suggest you offer all possible configurations (within the rating of the equipment that is)... field installed cord or factory installed cord with one plug configuration as standard and others as optional or simple variations.

What colours would you expect the cores of the cord to be?

Black/red/green preferred... but I believe the grounding wire must be green and the hots can be any color other than green or white, uncertain of but perhaps gray too. This is getting more into making a listed product than complying with the NEC, so outside my area of expertise [if you are so inclined to believe I possess such ].


For when neutral is used, same as above but add a white.

What about the same product, but now it does require the neutral. Should the plug be a NEMA 18-20? What do the markings X, Y, W & Z in drawing of the connector mean..... I guess the 3 phases plus neutral..... but Im not sure which is which!

You forgot "G" is also used...

W is always intended for a grounded conductor (typically a neutral conductor).

G is always intended for an Equipment Grounding Conductor (green)

I'm assuming you already have a plug/receptacle configuration chart. Do you also have the wiring diagrams? If not, PM me with your email address and I'll send you them. It is actually the Technical Information section of Leviton's L-100 catalog. Somehow I managed to get a pdf of just that section (1.14MB). Otherwise, you can download the whole catalog here. Forewarning: It is a 548 page catalog and 41.36MB in size.

 

[infinity]

any water heater I've ever seen came with an integral J box and a KO. It's not a motor so it doesn't require a disconnecting means. Most efficient just run a piece of flex to the WH.

What about 422.30?

 

[AdrianWint]

A big thank-you to you all for your responses so far...most enlightening.

A few replies to the comments so far....

any water heater I've ever seen came with an integral J box and a KO. It's not a motor so it doesn't require a disconnecting means. Most efficient just run a piece of flex to the WH.

The water heater itself is part of a bigger item of equipment, consisting of control equipment etc. This would be built up with a frame, control box etc and have one point of supply. Since the frame would be mobile we would like to supply power via a suitable flexible cord terminated in an appropriate plug.

Is this a fixed device or is it portable? If it's fixed I would expect something like this to come with a junction box where I could connect my own wiring appropriate to the installed location.

We prefer the use of a flexible cord & plug (assuming that it is acceptable to the country in question). Most equipment is transportable (ie. is fitted with wheels or castors) to allow it to be moved to different laboratories and also, from the UK culture, we like the idea of being able to clearly see that an item is disconnected from the power supply before performing any kind of maintainence. Using a plug & socket arrangement makes this isolation obvious.

Considering colors of the flexible cord sets. Whillis suggests that Brown, Blue, Green/yellow would be acceptable for a 120V cord set. These are the colours used for Uk flexible cords. We also have a cord set with Brown, Black, Grey, Blue, Green/Yellow cores. What would be your reaction if confronted with these on a piece of imported equipment you where asked to install? Would if throw you? Would you consider it to be wrong? Would it throw the average electrical contractor working for a school?


A final question for the moment.... here in the UK the IEC C15 connector is a common power input connector for equipment. I guess it might be known under another name in the US, but its the one that connects the power into the back of your PC. Obviously, in the UK we expect this connector to have 230V on it, but I guess in the US you expect it to have 120V present. Would it be wrong, therefore, for us to supply a lead with a NEMA 6-15 plug on one end & an IEC C15 on the other? I guess what I'm saying is if you found an IEC lead sitting on the desktop, would you expect it to be connected to a 120V supply or would you check first before plugging it into an item of equipment? Is there another connector that would be suitable (or commonly used) for this application in the US?

Thank you again for your time


Adrian

 

[don_resqcapt19]

...

Considering colors of the flexible cord sets. Whillis suggests that Brown, Blue, Green/yellow would be acceptable for a 120V cord set. These are the colours used for Uk flexible cords. We also have a cord set with Brown, Black, Grey, Blue, Green/Yellow cores. What would be your reaction if confronted with these on a piece of imported equipment you where asked to install? Would if throw you? Would you consider it to be wrong? Would it throw the average electrical contractor working for a school?
...
Adrian

The Brown, Black Grey, Blue, and Green/Yellow may be an issue for some electricians. Many of us know that you use blue in cords for the same purpose as we use white, however, in the NEC white and grey are used as grounded conductors. Seeing the grey, the electrician will likely use that as the grounded conductor and the blue as an ungrounded conductor.
If you are installing the plug on the cord and it is wired to our standards, then there is no reason for the electrician to even look at the cord colors and it should not be an installation issue for use. The only issue might be a listing issue with the agency that will be listing your equipment.

 

[augie47]

Adrian, allow me to approach a subject that I don't think has been discussed, and can be an interesting situation on "imported" equipment.
You are going to find some areas who only allow "listed" equipment to be installed. This pieces of equipment must bear the label of a Nationally Recognized Testing Lab (NRTL) such as UL, ETL, etc.
My experience has been that as a general rule, equipment that is cord and plugged equipped and "portable" does come come under scrutiny, but if your unit is to be "hardwired" or installed as a "fixed" piece of equipment, you might want to check the requirements for the specific location where it is being installed in regard to NRTL requirements.

 

[PetrosA]

A big thank-you to you all for your responses so far...most enlightening.

A few replies to the comments so far....




The water heater itself is part of a bigger item of equipment, consisting of control equipment etc. This would be built up with a frame, control box etc and have one point of supply. Since the frame would be mobile we would like to supply power via a suitable flexible cord terminated in an appropriate plug.



We prefer the use of a flexible cord & plug (assuming that it is acceptable to the country in question). Most equipment is transportable (ie. is fitted with wheels or castors) to allow it to be moved to different laboratories and also, from the UK culture, we like the idea of being able to clearly see that an item is disconnected from the power supply before performing any kind of maintainence. Using a plug & socket arrangement makes this isolation obvious.

Considering colors of the flexible cord sets. Whillis suggests that Brown, Blue, Green/yellow would be acceptable for a 120V cord set. These are the colours used for Uk flexible cords. We also have a cord set with Brown, Black, Grey, Blue, Green/Yellow cores. What would be your reaction if confronted with these on a piece of imported equipment you where asked to install? Would if throw you? Would you consider it to be wrong? Would it throw the average electrical contractor working for a school?


A final question for the moment.... here in the UK the IEC C15 connector is a common power input connector for equipment. I guess it might be known under another name in the US, but its the one that connects the power into the back of your PC. Obviously, in the UK we expect this connector to have 230V on it, but I guess in the US you expect it to have 120V present. Would it be wrong, therefore, for us to supply a lead with a NEMA 6-15 plug on one end & an IEC C15 on the other? I guess what I'm saying is if you found an IEC lead sitting on the desktop, would you expect it to be connected to a 120V supply or would you check first before plugging it into an item of equipment? Is there another connector that would be suitable (or commonly used) for this application in the US?

Thank you again for your time


Adrian

I would expect the IEC C15 to be 120V here. In theory, many computers/devices with this input might be rated for universal usage (self adapting transformers) but many are not. If it's feasible to order UL listed cord and have it installed at your end for the US/North America units, I would recommend doing so because the NEC reserves white and gray for neutral conductors. If not, and units will be field wired, I would make sure that your wiring is labeled L1 L2 L3 N and G (ground symbol) at the cord end and that connection terminals in the unit are labeled similarly as well.

Cheers,

 

[mpoulton]

We prefer the use of a flexible cord & plug (assuming that it is acceptable to the country in question). Most equipment is transportable (ie. is fitted with wheels or castors) to allow it to be moved to different laboratories and also, from the UK culture, we like the idea of being able to clearly see that an item is disconnected from the power supply before performing any kind of maintainence. Using a plug & socket arrangement makes this isolation obvious.

If it's intended to be mobile, flexible cord is a must. I would say anyone (UK or US) working on electrical gear would prefer "unplugged" to "turned off" when servicing it, so that's a plus.

I note you say this is a laboratory device, and mention schools. In that environment, a locking plug might be advisable. A NEMA L6-15, L6-20, or L14-20 (if neutral is needed) would be a good choice.

Considering colors of the flexible cord sets. Whillis suggests that Brown, Blue, Green/yellow would be acceptable for a 120V cord set. These are the colours used for Uk flexible cords. We also have a cord set with Brown, Black, Grey, Blue, Green/Yellow cores. What would be your reaction if confronted with these on a piece of imported equipment you where asked to install? Would if throw you? Would you consider it to be wrong? Would it throw the average electrical contractor working for a school?

Brown/Blue/Green is definitely fine. Plenty of equipment imported in the US is made with these colors in the cord, since many Asian manufacturers use it for all export goods. I have seen it commonly on both 120V and 240V equipment. I think just about any electrician could connect that, because the green is obviously ground and therefore the other two wires must be "power". If you don't need a neutral, this is the way to go.

That other color set, Brown/Black/Gray/Blue/Green, would be confusing for most US electricians I think. It is expected (mandated by the NEC, in fact) that gray or white wires are neutral. Using a gray conductor for anything but neutral would be counter intuitive in the US and would probably be installed wrong on a regular basis. It's worth noting that blue is a standard color for one hot on a 120/208V system here, so when presented with both a blue and a gray, Americans would undoubtedly try to connect the neutral to gray instead of blue. If I found that on something I were installing, I would have had to look it up online to find the proper connections (not anymore, I'll remember it now!). I think a significant percentage of electricians and institutional-plug-hooker-upper-type-guys would either get it wrong or be stumped.

A final question for the moment.... here in the UK the IEC C15 connector is a common power input connector for equipment. I guess it might be known under another name in the US, but its the one that connects the power into the back of your PC. Obviously, in the UK we expect this connector to have 230V on it, but I guess in the US you expect it to have 120V present. Would it be wrong, therefore, for us to supply a lead with a NEMA 6-15 plug on one end & an IEC C15 on the other? I guess what I'm saying is if you found an IEC lead sitting on the desktop, would you expect it to be connected to a 120V supply or would you check first before plugging it into an item of equipment? Is there another connector that would be suitable (or commonly used) for this application in the US?

Yeah, definitely don't put 240V on an IEC lead. I know it's commonly done elsewhere, and many scientific users here would know that, but in the US virtually all IEC connected equipment uses 120V. Few users would check before plugging a random IEC lead into any given device, possibly frying something if it weren't dual-voltage capable. Or they'll feed your device with 120V and call you to troubleshoot the problem...

 

[Besoeker]

Both of the nominal systems you describe are common offerings of our local utility, Austin Energy.

The only difference is that, here in Texas, we center-tap the winding.:grin:

Two nations divided by a common language?
I kinda have a foot in both camps with Mrs B being a southern belle.

Anyway, your post made me take a light hearted look at some of the differences.

 

[nakulak]

I'm curious - what type of educational teaching equipment comes with a built in water heater ?

 

[LarryFine]

I'm curious - what type of educational teaching equipment comes with a built in water heater ?

Why, the Acme Water-heater Educational Teaching Demonstrator kit, of course!

 

[dbuckley]

One of the oddest differences betwixt these two great nations is that neutral conductor.

neutral (UK, USA under duress!) = grounded conductor (USA)

There in an implication in the use of "grounded" (sounding like "ground") that the neutral is the same as the ground. However in the UK all conductors that are not actually earth conductors (ie identified green/yellow or maybe gree for older installations or bare wire sometimes) are to be treated as live conductors.

Also Romex being a brand name for a type of NM (non-metallic) sheathed conductor - A UK sparky would recognise that type of cable generically as T&E (twin and earth) though there are variants with more than two current carrying conductors. An Australian or New Zealander would call it TPS (Thermo Plastic Sheathed).

I've been on this forum as a non-American for ages now, and still every day I learn some new oddity difference between "The American Way", "The UK way", "The NZ way", and "Elsewhere in the world" ways. I continue to find it facinating...