ROBERT via EV wrote:

> Roger, let me try to clarify my concern.  A person buys a third party
> J1772 to NEMA adapter (made in China and made cheap).  The adapter has a
> NEMA rated 20A plug.  The adapter does not produce a modified pilot
> signal.

Just to be clear, the adapter does not (*cannot*) produce a modified pilot 
signal since the NEMA outlet has no provision for a pilot signal connection and 
the charger that plugs into the NEMA outlet does not require a pilot signal.  
The pilot signal *from* the J1772 EVSE is one-way only; that is, it is 
generated by the EVSE to inform the load of the maximum current that may be 
drawn *at that particular time* (i.e. while the EVSE may be capable of up to 
50A, it is possible for it to limit the current available to the load to any 
value less than this at any time).  There is no way for a J1772 charger or 
adapter connected to the EVSE to tell the EVSE to reduce the maximum available 

> I take the cord and plug from the EVSE that is rated at 50A and
> plug into the adapter.  I take the 20A coil and plug from the charger in
> my converted car and plug into the adapter.  The charger will not draw
> more than 20A from the EVSE.  This is OK load wise because the EVSE can
> output 50A.  However, it is an unsafe circuit.  I have connected a 50A
> rated source to a 20A circuit with no interconnecting protection
> device.

I understand your concern with this configuration now.  I agree that the EVSE 
breaker will not provide adequate protection for a lower current rated 
J1772-to-NEMA adapter connected between the EVSE and the load (charger).  Note 
that this scenario is irrelevant in the situation where a NEMA outlet is 
provided at each parking spot as the charging infrastructure (which is what was 

Note also that any charger with any safety agency (CSA, UL, etc.) listing 
*will* have a protection device at its input appropriately rated to protect it. 
 In this case the safety concern reduces to a user who tries to use an adapter 
that is under-rated for their charger (but still does not apply to the 
situation of a NEMA outlet charging infrastructure).
> Lets go the other direction.  I have a NEMA to J1772 adapter
> with no pilot signal.

This situation is *not* possible.  The reason you have a NEMA to J1772 adapter 
is to provide a J1772 connection to the charger, and the J1772 charger 
*requires* a pilot signal from the EVSE ("adapter", in this case).  The adapter 
*must* provide a pilot signal, the only question is if it provides a pilot 
signal that is appropriate for the rating of the NEMA outlet/circuit that it is 
plugged into.

> If the cable from the adapter is plugged into a car
> with a 50A charger, the circuit breaker will trip

No.  Since the J1772 charger requires a pilot signal, and the EVSE/adapter must 
provide one, the 50A rated charger will draw no more than the amount of current 
signalled by the pilot signal.  In the absence of a pilot signal, the charger 
will not draw *any* current.

The only safety concern when using a NEMA to J1772 adapter is that the adapter 
might generate a pilot signal that allows the charger to draw more current than 
the NEMA outlet/circuit it is plugged into is rated for.

This should not occur for any competently designed adapter.  As I described in 
my prior post, if a 120V NEMA to J1772 opportunity charge cord (adapter) has a 
5-15P NEMA plug at the wall end, then it "knows" that no matter what the supply 
circuit it is powered from might be rated for (i.e. 15A or 20A), it cannot 
allow the load to draw more than 12A since its own connector is only rated for 
15A (and such a circuit is limited to 12A max continuous loading).  If it has a 
5-20P NEMA plug at the wall end, then it "knows" that it can allow the load to 
draw up to 16A since its connector (and wiring) are rated for 20A and it can 
only be plugged into a receptacle/circuit rated for 20A.

In the event of use of an incompetently or unsafely designed adapter that 
generates a pilot signal allowing the charger to draw more current than the 
NEMA outlet it is powered from can safely deliver, the protection device 
between the supply and the NEMA outlet will trip and safely protect all 
connected devices.

I think that there is actually very little safety concern with a NEMA outlet 
charging infrastructure since the vast majority of people using NEMA to J1772 
adapters will be owners of OEM EVs and using the OEM opportunity charge cord 
provided by the OEM (i.e. competently designed adapters).

The main advantage of the NEMA outlet infrastructure, IMO, is that there are no 
charge cords left at each parking stall to be vandalised or stolen, however, 
the big disadvantage is that the vast majority (is anybody still building 
conversions?) of EVs that will use the charging infrastructure *don't* have 
NEMA connectors, but rather J1772 charge inlets.  So, each EV must carry around 
a NEMA to J1772 opportunity charge cord/adapter to plug in and must somehow 
secure this relatively expensive cord so that it is not stolen while the car is 

I think it would be relatively difficult to get support for installation of a 
new NEMA outlet-based charging infrastructure, and that there is probably an 
opportunity here for an inexpensive *level 1* J1772 charging station that could 
be installed in place of each NEMA outlet.  Ideally, someone would come up with 
an EVSE that does not have a permanently attached J1772 charge cord, but 
instead allows (requires) the user to first connect their own charge cord to 
the (de-energised) EVSE, and then plug the J1772 paddle into the vehicle 
receptacle.  A possibility is for the EVSE to have a receptacle into which the 
user's cord plugs that is equipped with a secure cover that can be closed to 
prevent the user's cord from being unplugged.  Provide an interlock such that 
the receptacle is de-energised when the cover is open, and a solenoid or other 
securing mechanism that prevents the cover from being opened after the J1772 
paddle is mated to the vehicle receptacle and is energised by the EVSE.



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