LeftieBiker
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Re: Dryer Plug Adapter for Leaf 2020 Plus EVSE

Sun Apr 11, 2021 11:15 am

sdbmania wrote:
Sun Apr 11, 2021 10:44 am
I have an electrician who yesterday installed a new plug for a new dryer I'm getting on Tuesday. He suggested replacing the 30 amp breaker for it with a 60amp and then diverting 20amps to the dryer and the other 40 for the car via a new outlet. That way I can use both the dryer and charge the car at the same time. Considering that, but the manual says the dryer requires 30 amps. So, I wasn't sure what the actual power draw was. Guess the worst case would be just using one at a time.
That sounds like a great way to effectively remove the protection the breaker offers, giving both the dryer and the EVSE the opportunity to start a fire if either develops a wiring issue other than a full-on short. And yes, both do require 30 amps each. You have a 24 amp EVSE that needs a 30 amp circuit, and a roughly 24 amp dryer that requires the same. Two half-sized 30A breakers, each with its own wiring, may work, but one 60A breaker will not.
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jjeff
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Re: Dryer Plug Adapter for Leaf 2020 Plus EVSE

Sun Apr 11, 2021 11:24 am

sdbmania wrote:
Sun Apr 11, 2021 10:44 am
I have an electrician who yesterday installed a new plug for a new dryer I'm getting on Tuesday. He suggested replacing the 30 amp breaker for it with a 60amp and then diverting 20amps to the dryer and the other 40 for the car via a new outlet. That way I can use both the dryer and charge the car at the same time. Considering that, but the manual says the dryer requires 30 amps. So, I wasn't sure what the actual power draw was. Guess the worst case would be just using one at a time.
When you/he? said "replacing the 30a breaker with a 60a" I would assume he was also planning on new 60a wiring? Also no way to really "divert" 20a to the dryer and 40a to something else, it's a 60a breaker well unless you also add a sub-panel with a 40a breaker and 20a breaker, feeding the 40a breaker to your EVSE and 20a breaker to your dryer.
If the dryer manual says 30a it means it should be on a circuit capable of short-term 30a draw but no less than a 24a continuous rating, the dryer needs to have a 30a breaker. As far as the EVSE breaker, assuming you have a Leaf that can draw 27.5a then you'll need a minimum 40a circuit/breaker for continuous use. As dryers and EVs are both continuous draw you'd add 24a+27.5a=51.5a which would be too much for a 60a circuit which maxes out at 48a continuous, not sure what your electrician was getting at....
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alozzy
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Re: Dryer Plug Adapter for Leaf 2020 Plus EVSE

Sun Apr 11, 2021 12:19 pm

Find a better electrician, yikes!
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knightmb
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Re: Dryer Plug Adapter for Leaf 2020 Plus EVSE

Sun Apr 11, 2021 12:19 pm

jjeff wrote:
Sun Apr 11, 2021 11:24 am
As dryers and EVs are both continuous draw you'd add 24a+27.5a=51.5a which would be too much for a 60a circuit which maxes out at 48a continuous, not sure what your electrician was getting at....
Not to start an electrician forum war about loads and safety margins ;) , but if the cable run is really short, say the breaker box is right next to the dryer outlet for example, then in theory it would be safe. The reason that the safety run of thumb is 80% is to account for resistance over distance that you don't know for any household. So if the cable was being run 6 feet vs 60 feet, the wire can handle the *power* at that short of distance, but probably not at 60 feet if the two were just so far apart. Having said that, the electrician should know what they are doing and we don't know how the wiring is setup, so I would error on the side of the electrician unless we have some more details about how the house is wired. Just my experience and what I learned in college, take it as an opinion though...

Edit: Changed load to power because there is a big difference in regards to safety and breakers and this is only in reference to pure power and heat generation.
Last edited by knightmb on Sun Apr 11, 2021 1:39 pm, edited 1 time in total.
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wwhitney
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Re: Dryer Plug Adapter for Leaf 2020 Plus EVSE

Sun Apr 11, 2021 12:38 pm

rpiotro wrote:
Sat Apr 10, 2021 7:10 am
With all of this discussion about simply upgrading the plug to a 10-50 "RV" plug and installing a 40 or 50 amp breaker
NEMA 10 receptacles are ungrounded (no EGC) and should never be used for new circuits, as an EGC is required. The only acceptable use I'm aware of is like for like replacement on existing ungrounded circuits (e.g. dryer or stove). New circuits should be NEMA 6 (240V only) or NEMA 14 (120V/240V).

Cheers, Wayne

wwhitney
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Re: Dryer Plug Adapter for Leaf 2020 Plus EVSE

Sun Apr 11, 2021 12:42 pm

sdbmania wrote:
Sun Apr 11, 2021 10:44 am
I have an electrician who yesterday installed a new plug for a new dryer I'm getting on Tuesday. He suggested replacing the 30 amp breaker for it with a 60amp and then diverting 20amps to the dryer and the other 40 for the car via a new outlet.
That is a fine solution if and only if it includes a small new panel at the load end of the 60 amp circuit, with a 30amp breaker for a NEMA 14-30 dryer receptacle and a 40 amp breaker for NEMA 6-50 or 14-50 receptacle for the EVSE. The 60 amp breaker may at risk of nuisance tripping depending on the details of the load calculation; not familiar with electric dryer specs off the top of my head.

Cheers, Wayne

wwhitney
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Re: Dryer Plug Adapter for Leaf 2020 Plus EVSE

Sun Apr 11, 2021 1:03 pm

knightmb wrote:
Sun Apr 11, 2021 12:19 pm
Not to start an electrician forum war about loads and safety margins ;) , but if the cable run is really short, say the breaker box is right next to the dryer outlet for example, then in theory it would be safe. The reason that the safety run of thumb is 80% is to account for resistance over distance that you don't know for any household.
Nope, wire resistance has nothing to do with the 125% factor for continuous loads (a.k.a. 80% maximum continuous load on a breaker) in the NEC. Rather it is a reflection of the mismatch between the current vs time trip curve characteristics of thermal magnetic breakers, compared to the current vs time damage curve of installed conductors.

A breaker's trip curve is selected to protect a conductor with ampacity equal to the breaker's rating against overloads of all time periods (short duration overloads are intentionally allowed, e.g. to allow for motor starting current). It turns out that short duration protection controls the selection of trip curve, and a side effect is that the thermal magnetic breaker will trip too aggressively at long durations. E.g. if you need a 30A breaker to trip within 3 seconds at 100A (to make up some numbers), then a side effect will be that it may trip at 27A after 4 hours.

So for a continuous load you must upsize the breaker to avoid the possibility of nuisance trips. And then since the breaker has been upsized, the conductors must be as well, so that they are still adequately protected by the breaker.

Cheers, Wayne

P.S. The NEC specifies that an electric dryer be considered for load calculations at the greater of the nameplate rating or 5000W. Electric dryers are not continuous loads. I looked at a few spec sheets and 5600W seems to be a common rating for 240V dryers, i.e. 23.3A. For a 60A feeder for both such a dryer and an EVSE, that would leave headroom for a 29A EVSE; not quite compliant to wire a 30A EVSE with a 5600W dryer on a 60A feeder, although the risk of nuisance tripping would be low.

knightmb
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Re: Dryer Plug Adapter for Leaf 2020 Plus EVSE

Sun Apr 11, 2021 1:37 pm

wwhitney wrote:
Sun Apr 11, 2021 1:03 pm
E.g. if you need a 30A breaker to trip within 3 seconds at 100A (to make up some numbers), then a side effect will be that it may trip at 27A after 4 hours.

So for a continuous load you must upsize the breaker to avoid the possibility of nuisance trips. And then since the breaker has been upsized, the conductors must be as well, so that they are still adequately protected by the breaker.
I should have clarified, I was referring to the wire itself when it comes to heat being generated at dangerously high temperatures for the amount of power being sent through it, but your explanation is much more precise and having the breaker nuisance trip all the time is certainly something that would get annoying quickly.
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wwhitney
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Re: Dryer Plug Adapter for Leaf 2020 Plus EVSE

Sun Apr 11, 2021 1:57 pm

knightmb wrote:
Sun Apr 11, 2021 1:37 pm
I should have clarified, I was referring to the wire itself when it comes to heat being generated at dangerously high temperatures for the amount of power being sent through it,
In practice, the limitations of the breaker and of the connections at the ends of the wire always control over the wire's current handling ability itself, absent elevated temperatures or bundled conductors. For example, 2017 NEC table Table 310.15(B)(16) tells us that the ampacity of 90C insulated #10 copper is 40A. That means that when 3 conductors of that size are near each other (in the same cable or raceway) they can reliably carry 40A without overheating insulation rated for 90C use.

[Going back to your 6' vs 60' example, if the portion of the wire outside the terminations is operating all under the same condition (e.g. run through fiberglass backs and wood studs), I would expect the temperature for the wire to be the same along most of its length. There will be some end effect that extends beyond the terminations, and possibly the end effect is longer than 3', so a 6' run would differ from a 60' run, but maybe once you reach 10' and up, the worst case in the middle of the run will be the same independent of length.]

But you will almost never see #10 Cu wire on a 40A breaker, because for most applications it is limited to 30A by the small conductor rule. [Motor circuits, e.g. HVAC, is one exception, but there the 40A breaker would not be providing overload protection, it's just providing short circuit and ground fault protection.] And even when it's not it would be extremely rare to be able to use #10 at its full 90C ampacity, as terminations are generally limited to 75C at best, for which #10 Cu has an ampacity of 35A.

Cheers, Wayne

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Re: Dryer Plug Adapter for Leaf 2020 Plus EVSE

Sun Apr 11, 2021 3:34 pm

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