Do It Yourself: 240v from two 120v sources

[MikeD]

The following two NEC articles relate to the "125% continuous load rule(s)":

2011 NEC Article 210.20(A) (Overcurrent Protection -- Continuous and Noncontinuous Loads): "Where a branch circuit supplies continuous loads or any combination of continuous and noncontinuous loads, the rating of the overcurrent device shall not be less than the noncontinuous load plus 125 percent of the continuous load."

2011 NEC Article 625.14 (Rating) "Electric vehicle supply equipment shall have sufficient rating to supply the load served. For purposes of this article, electric vehicle charging loads shall be considered to be continuous loads."

The following two NEC articles relate to the "80% max receptacle load rule" (which apparently attempt to minimize the risk of overloading due to one big load on a multi-receptacle branch circuit), but is still probably good to know and respect:

2011 NEC Article 210.23(A)(1) (Permissible Loads -- 15- and 20-Ampere Branch Circuits -- Cord-and-Plug-Connected Equipment Not Fastened in Place): "The rating of any one cord-and-plug-connected utilization equipment not fastened in place shall not exceed 80 percent of the branch-circuit ampere rating."

Article 210.21(B)(2) (Outlet Devices -- Receptacles -- Total Cord-and-Plug-Connected Load)
which is similar in purpose to the one just above and limits total load for a given receptacle to 80% of the branch circuit rating.

I am essentially asking why does the NEC have the above 125% rule for "Continuous Loads" (which appears to apply to EVSEs even for charging sessions less than 3 hours because of Article 625.14 above)? Any licensed electricians (or any others) who work with residential wiring for a living have some knowledge/insight they would like to share? I'm trying to elicit some understanding of this issue for the benefit of us all, not just be authoritative and quote NEC articles w/o the substance behind them -- and I apologize if my previous post offended people in its approach to raising the issue.

 

[davewill]

How about you get to the point of your question instead of asking passive aggressively?

He has no point. He just likes hassling anyone posting about the EVSE Upgrade. Classic concern trolling.

 

[Ingineer]

He has no point. He just likes hassling anyone posting about the EVSE Upgrade. Classic concern trolling.

Most of the active members here, including myself, have simply added him as a "foe". Simply click on his profile, then "add Foe" and then all his posts go away. Unfortunately I still see his posts whenever someone quotes him. (Luckily, this is getting much more infrequent, as he is already invisible to most!)

All I can assume is that he has some business interest that is being negatively affected by my efforts and is trying to discredit me and anything I do. Sadly, He seems to want to continuously engage FUD, which is detrimental to the whole EV movement in general.

-Phil

 

[MikeD]

Ingineer: No, I am retired. I have no interest in attacking anyone or imputing their motives in my posts. I prefer to discuss issues based on reasoning and whatever facts can be determined, and leave it at that. One issue that I post a lot about is concerning charging safety. I don't consider myself an expert in this area, credentialed or otherwise, but being retired I am trying to learn what I can which included taking a class from a local inspector on the 2008 NEC before I got my 2011 Leaf.

If I can post something that is of value to others -- great! But I know I'm not a skilled communicator and what I post may not be of interest to many, and regretfully, even irritating and of course many may disagree on certain matters. For better or worse I also will "challenge authority" at times if it seems to me appropriate. You, for example, have posted that forum readers "trust" you in your posts. I would never post that about myself. I welcome any and all criticism about the substance of my posts -- including yours.

Thanks for responding to my previous recent posts in this thread; but of course I would prefer if you also say something about any reservations or recommendations, if any, you have to anyone using the 2013 EVSE Upgrade together with a "Quick 220"-like device.

 

[QueenBee]

I am essentially asking why does the NEC have the above 125% rule for "Continuous Loads" (which appears to apply to EVSEs even for charging sessions less than 3 hours because of Article 625.14 above)? Any licensed electricians (or any others) who work with residential wiring for a living have some knowledge/insight they would like to share? I'm trying to elicit some understanding of this issue for the benefit of us all, not just be authoritative and quote NEC articles w/o the substance behind them -- and I apologize if my previous post offended people in its approach to raising the issue.

Fair enough. IMO the reason EVSEs are to be considered continuous loads is just the fact that one might try to say that a portable EVSE is only going to be used lightlyand not left in place for more than a couple hours but it's easy to forget. Or one could say well my EV always charges to full in 2 hours because it has a small battery so the 125% rule doesn't apply, until the day a different EV is connected. This rule just avoids any issue with trying to use that logic.

As to what exactly the 125% rule is intending to do. I think this is a very good question. What exactly are the consequences of a continuous load at 100% of a circuit's design? Obviously one answer is that it might just be an extra bit of caution to be applied ahead of time when loads are known to be at limit of a circuit. If that was the case I would think that the ampacity rules for wire could just be decreased to include this extra margin. Additionally if you look at the rules regarding 100% continuous load rated circuit breakers you'll see that when they are used the 125% rule does not apply to the wire.

I would surmise that instead the 125% rule is there to protect (And allow them to operate properly) circuit breakers which are only designed to handle 80% continuous loads. My idea being that our standard circuit breakers have two trip mechanisms. One being the electromagnet feature that kicks in once the amperage is high enough and the other being the bimetallic strip which is based entirely on the heat that amperage causes. Passing a 100% continuous load through a circuit breaker that is only rated for 80% continuous load could have two problems. The first being prematurely tripping caused by the extended use causing heat to build up. Then the second that this extended heat may also have the possibility of damaging and/or lowering the life span the circuit breaker. The additional tripping would obviously be poor design from a user POV and would also impact the lifespan of the breaker.

So my guess is this rule is there to handle the limitations of our 80% rated circuit breakers and is not there to protect the wiring.

On a related note: I'm not sure if this is the case with all disconnect switches but my 60 AMP disconnect is rated for 100% continuous load. So another question is what other components of a electrical system are not rated for 100% continuous load at their given rating? Are 15 amp receptacles rated for 100% load, etc, etc.

 

[Ingineer]

The 125% rule was instituted after a number of reports of fires and damaged systems were found to have been caused by high continuous loads. A non-continuous load allows time for heat to be dissipated or absorbed into the thermal mass, but a continuous load may not. The main problem is external factors affecting a system originally engineered to handle 100% loads, with the main one being improper termination, but also there are factors such as oxidation, mechanical faults, thermal cycling, etc., so they decided to basically enlarge the safety factor. In all truth, your insurance company doesn't care if your electrical system now costs more, as long as it is as safe as practical and generates zero claims. For those that don't know; The NEC is written by the NFPA which is made up primarily of insurance companies, so their primary goal is to reduce claims.

When they implemented the 125% rule, they allowed for a "loophole" of sorts:

Exception: If the assembly, including the overcurrent devices protecting the branch circuit(s), is listed for operation at 100 percent of its rating, the allowable ampacity of the branch circuit conductors shall be permitted to be not less than the sum of the continuous load plus the noncontinuous load.

This basically means that as long as all of your equipment used in a circuit is specifically rated for 100% duty, then you can omit the 125% over-spec requirement.

If you compare a standard electrical device with it's 100% rated counterpart, you usually see bigger and better-designed terminals, and features such as wire clamping plates instead of a simple screw terminal. You also never see the "Stab-lock" or equivalent rear-wiring systems used on 100% spec-grade devices.

When I re-engineered the EVSE upgrade, I decided to be as safe as practical, so I specified better choices even if they cost a little more. I went with a 100% rated molded 240V plug and cable assembly, rather than a screw-on. In this molded plug all the connections between the wire and the plug pins are actually welded instead of soldered or crimped. This lowers the resistance and helps ensure there is less heat generated when under high loads. I have seen countless screw terminal devices fail with high resistance and subsequent burning, so it's best to steer clear of them if practical. Unfortunately it's not practical to use welded joints on your home wiring, but the next best thing is to use high-spec-grade devices and oversize your wiring by at least one gauge size. Consequently I recommend all EV owners have the upgraded wiring sizes along with high-spec outlets installed for EV charging. This only incurs a small incremental cost in most cases, so it's still a practical choice and won't obliterate your wallet.

-Phil

 

[MikeD]

For whatever it's worth, I just read the following summary for a proposed new Article for the next (2014) NEC:

"210.17 Electric Vehicle Branch Circuit: The proposed new section to Article 210 (Branch Circuits) would require that outlet(s) intended for the purpose of charging electric vehicles be supplied by a separate, dedicated branch circuit."

Nissan has always recommended a dedicated circuit be used for its portable, level 1 EVSE -- which BTW also implies a "single" receptacle and not the much more common "dual" receptacle. When implemented this, of course, eliminates the possibility of overload due to additional receptacle loads on the same branch circuit as the EVSE.

This change should help discourage "Quick 220"-type device use, since most receptacles (even ignoring a second plug outlet on a "dual" receptacle) are not dedicated.

 

[MikeD]

Ingineer: Thanks for your just previous post concerning NEC's "125% rule". I'm sorry, however, that you did not also say something about your EVSE Upgrade product in connection with the OP's topic -- so I respectfully request that you do so.

On another related point concerning your products, you also sell a "5-15 to L6-30 Adapter" (Model: A15L30), UL Listed adapter, presumably intended to be used with the 2013 EVSE Upgrade which allows selecting a 16a 120v charging current. Is the 5-15 plug listed for use as high as 16a? I ask because all the Nema 5-15 products that I recently looked at are only rated/listed at 15a. I really don't think it is significant if it is not rated that high, after all it is just one amp! Regardless, in connection with this post regarding "Quick 220"-like products it brings to mind that with your 2013 Upgrade used together with a "Quick 220"-like device, one can inadvertently draw up to 20a 120v through 5-15 plugs and receptacles, and likely none are rated/listed for more than 15a -- a 5 amp difference which IS potentially significant.

 

[sorphin]

Ummm... What would happen if my Wife plugged the toaster in without first flipping the switch? Is the concern here too much current. I mean the toaster wouldn't see 240 volts would it? :shock:

You can't plug a toaster into an L6-20 outlet. This is why I'm absolutely adamant that you never use a 120V outlet to carry 240V in any scenario. I always ensure that it's the reverse; we use an L6-20 or L6-30 on the EVSE so that it will only fit into a 240V plug, then provide an adapter from a standard 120V outlet to the L6-20. The only way you could mess this up is to deliberately install an L6-20 on your toaster, which would be a bad idea.

-Phil

But you could make toast twice as fast! *smirk*

 

[Ingineer]

But you could make toast twice as fast! *smirk*

Actually, it would be about 4 times faster! Assuming a 10 ohm resistance of your typical toaster, it's 1.44kW on 120v, but when plugged into 240v, you get a whopping 5.76kW! People are too used to thinking in terms of fixed amps. That 10 ohm toaster will pull 12A on 120V, but on 240v it'll pull 24A! The amps double along with the voltage, so you get 4 times the power.

-Phil

 

[sorphin]

But you could make toast twice as fast! *smirk*

Actually, it would be about 4 times faster! Assuming a 10 ohm resistance of your typical toaster, it's 1.44kW on 120v, but when plugged into 240v, you get a whopping 5.76kW! People are too used to thinking in terms of fixed amps. That 10 ohm toaster will pull 12A on 120V, but on 240v it'll pull 24A! The amps double along with the voltage, so you get 4 times the power.

-Phil

This is true.. Though I doubt the nichrome wire would even withstand it!

 

[davewill]

But you could make toast twice as fast! *smirk*

Actually, it would be about 4 times faster! ...

Yeah. I really like the way a simple electric kettle full of water can get to a boil really quickly in Europe. Here there's almost no point to owning one.

 

[mwalsh]

Yeah. I really like the way a simple electric kettle full of water can get to a boil really quickly in Europe. Here there's almost no point to owning one.

Hairdryers too! Hating on my 120v hairdryer a lot, now I'm back in the States from Europe! :x

 

[QueenBee]

The 125% rule was instituted after a number of reports of fires and damaged systems were found to have been caused by high continuous loads. A non-continuous load allows time for heat to be dissipated or absorbed into the thermal mass, but a continuous load may not. The main problem is external factors affecting a system originally engineered to handle 100% loads, with the main one being improper termination, but also there are factors such as oxidation, mechanical faults, thermal cycling, etc., so they decided to basically enlarge the safety factor. In all truth, your insurance company doesn't care if your electrical system now costs more, as long as it is as safe as practical and generates zero claims. For those that don't know; The NEC is written by the NFPA which is made up primarily of insurance companies, so their primary goal is to reduce claims.

Phil, any hints on where you learned this history? I'd like to read more as to why this rule was created. I know it's out there but my googling just hasn't returned it yet.

 

[Ingineer]

Phil, any hints on where you learned this history? I'd like to read more as to why this rule was created. I know it's out there but my googling just hasn't returned it yet.

I don't keep detailed account of all my knowledge sources over the years. It's hard enough just to keep the take-away!

Here is history of the NEC.

-Phil

 

[QueenBee]

Phil, any hints on where you learned this history? I'd like to read more as to why this rule was created. I know it's out there but my googling just hasn't returned it yet.

I don't keep detailed account of all my knowledge sources over the years. It's hard enough just to keep the take-away!

I can certainly understand that! The issue I keep running into is I trust your experience and knowledge more than many of the sources of tidbits of information I've gleaned thus far.

To summarize my theory: The 125% continuous load rule's primary goal is to prevent the temperature of circuit breakers from increasing such that they trip at a lower rating than is needed to protect the wiring. This obviously has the added benefit of creating a more robust circuit because the increased circuit breaker size requires that the wire ampacity rating be increased which increases the safety margin.

The main reason why I think the distinction of the history is important and of interest to me is in cases where we are continuously but not permanently pushing a circuit to 100%. If the NEC's primary concern with that is that it will cause the circuit breaker to trip then I'm a whole lot more comfortable doing this. If on the other hand the NEC's primary concern is that the circuit will not be able to handle a 100% continuous load and thus the risk of damaging the circuit and burning down the building that's not so good. Obviously if there are issues with the circuit such as bad terminations, damaged wire, worn out receptacle, etc. additional damage and fire could happen from only an 80% continuous load.


I found this bit from JADE learning: http://www.jade1.com/jadecc/registration/JADE_HS_PDFbuilder.php?courseDB=UNIVERSAL&varID=OCURPROT_ACC11_V2&state=UT&trade=Electrical&course=OCURPROT_ACC11_V2_HS&content=No&contentNumbers=Yes&questions=Yes&questionNumbers=Yes&output=PDF&expDate=5/25/2013" onclick="window.open(this.href);return false;

The problem with continuous loads is the heat that is generated in both conductors and in terminals where conductors are connected. Heat is produced any time current flows through conductors and through terminals; but, if conductors are sized correctly and the loads do not run continuously the head produced is insignificant. However, the longer the current flows through a conductor or through terminals where it is connected the more they are heated. The NEC has found that loads operated for 3 hours or more cause significant heat to build up which adversely affects conductors, terminations, and overcurrent devices. Increasing the rating of overcurrent devices and the ampacity of conductors for continuous loads by 125% compensates for the heat buildup at the overcurrent device terminals.

Circuit breakers are thermal-magnetic devices; and, increased heat at the breaker terminals can cause a breaker to trip at a current below the breaker's rating. A larger breaker will compensate for the heat build up of continuous loads by having a higher thermal trip point. A circuit breaker's thermal setting is to protect the circuit from overloads, not short circuits. Additional heat at the breaker terminals will fool the breaker into thinking there is an overload on the system and cause a nuisance trip.

 

[hieuous]

I need to do this as i'm living at a rental house and installing a 240v isn't practical...I've been reading post after post but i'm still not sure if i have a good grasp of this. I definitely want to do this though, i always take more pride in my own work.

can somebody type up or take a picture and do a guide? i'm trying to understand the schematic on page one but it's been years since i've even looked at a schematic.

 

[JimSouCal]

I need to do this as i'm living at a rental house and installing a 240v isn't practical...I've been reading post after post but i'm still not sure if i have a good grasp of this. I definitely want to do this though, i always take more pride in my own work.

can somebody type up or take a picture and do a guide? i'm trying to understand the schematic on page one but it's been years since i've even looked at a schematic.

As discussed somewhere (maybe in this thread?) there are units for sale ($210+tax shipping) that might free up your time unless you like the idea of making it yourself. http://www.quick220.com/220_catalog/20-ampere-systems-locking.html" onclick="window.open(this.href);return false;

 

[hieuous]

I need to do this as i'm living at a rental house and installing a 240v isn't practical...I've been reading post after post but i'm still not sure if i have a good grasp of this. I definitely want to do this though, i always take more pride in my own work.

can somebody type up or take a picture and do a guide? i'm trying to understand the schematic on page one but it's been years since i've even looked at a schematic.

As discussed somewhere (maybe in this thread?) there are units for sale ($210+tax shipping) that might free up your time unless you like the idea of making it yourself. http://www.quick220.com/220_catalog/20-ampere-systems-locking.html" onclick="window.open(this.href);return false;

i saw that but it looks easy enough, i want to tackle it on my own.

i know there are a couple "guides" here but none of them really show what to connect and what not to connect.

 

[mwalsh]

i know there are a couple "guides" here but none of them really show what to connect and what not to connect.

There is a schematic on here someplace and there were plenty of photos accompanying it in the thread. I also believe a schematic for the relays is available online too, With all due respect, if you aren't able to read these types of things, you should probably reconsider building a DIY box.