L6-20P -> L6-30R

I have a situation where a 208v/20A PDU (L6-20P) is supposedly hooked to a 208v/30A circuit (L6-30R). Before I order the correct PDU's and whip cords...sanity check...are connectors 'similar' enough that this is possible (with force) or am I going to find we've actually got L6-20R's on the provider side?

Generally, all common electrical plugs and receptacles (straight-blade, twist-lock, IEC, and CEE) are physically sized and keyed differently, so that they can't be connected together, to keep people from connecting loads that require a specific voltage/current to supplies that aren't intended to provide it.

While it's not uncommon for someone to replace a plug with "the right kind", this can (in order of badness):

1. start a fire
2. short out and (hopefully) trip a breaker - that's what breakers are for!
3. violate building/electrical codes
4. void your device's warranty

As others have mentioned, just "making it work", rather than making it work correctly, can be bad news.

People often fancy themselves unlicensed/uncertified electricians. I've seen some of the handiwork from such people, and while their creativity is impressive, having to rip their stuff out and re-do it is not fun.


They're different. You can't force them.

The whole point behind the locking connectors (like the IEC
connectors) is to prevent you from plugging the wrong connectors
together. Not only are the different dimensions, but the prongs are
keyed differently as well.

If you put a L6-20P device into a L6-30R, then it was done by
physically replacing the plug on the PDU, not by "making it work".

I have had to do this at times but it is not strictly allowed by
codes and not at all recommended.


‎The connectors are definitely distinct and incompatible, you won't be able to force a 20 into a 30 or vice versa.

So yes, one of the ends has been changed.


Original Message

* web@typo.org (Wayne E Bouchard) [Tue 18 Mar 2014, 23:53 CET]:

I have had to do this at times but it is not strictly allowed by codes and not at all recommended.

It's an active fire hazard. The cables aren't rated (= built) for the power draw.

  -- Niels.


I think the 250 v 15 amp plugs fit in the 20 amp sockets, but the 20s don't
fit in the 30 sockets.

This sort of thing is usually an adapter, a little cylinder with a L6-20R
on one end and a L6-30P on the other, since the loads are safe. Either
that, or a short jumper cable wired the same way.

They are slightly different.


Crap, was looking at the non-locking ones. Ignore that.

I've had to do that before; provider gave me a 208v/30a circuit and I
already had a power strip I wanted to re-use that had a corded L6-20P
connector on it. I purchased a L6-30P plug / L6-20R receptacle adapter
from http://www.stayonline.com/nema-locking-6-30-amp-adapters.aspx
They're only $25 and they ship overnight if needed. They have one foot
cabled versions of the same thing too if you have tight working space
and there's not enough room for both connectors back to back; works as a
strain relief too so maybe that option is better regardless.

If you're trying to go the other direction, plugging an L6-30P into an
L6-20R 20 amp circuit, that I'd recommend against because it never fails
that someone says hey, 30 amp power strip, let me plug some more stuff
into it not realizing it's on a 20 amp breakered circuit, then all your
stuff goes down while you try to find the facility staff to reset the


As it happens, the chart at


suggests that the L6-20 and L6-30 are less different than you'd expect.

I *think* those are on different diameters, and a datacenter employee ought
to friggin' know better... but I don't think it's 100% impossible that this
has happened.

If it did, you're gonna replace the plug anyway...

As long as there's a 20A breaker on the PDU, you're safe, if not within

-- jra

That's a problem in the other direction, but plugging a 20A device into
a 30A feed shouldn't be a hazard at all.


Strictly speaking, no, you cannot do this. The diameter of the pattern of the pins are different 20 to 30 amps.

If no electrical inspectors are looking, yes, you can bend the pins and "make it work." I've done it, others have done it, but you shouldn't do it and it is a clear electrical code violation.

Go to Lowes or Home Depot, but the right end, and stick it on there. You do still have the issue where the wire size is wrong, but if you have a brain and don't overload it, you will be OK. But, this too is still a clear electrical code violation.

Go look at any standard household lamp. It has a 5-15P on the end of it, which could be plugged into an outlet rated for 20 amps (5-20R), with 16 gauge lamp cord rated for 10 amps or less.

It all depends on the connected load.

I plan on installing the correct PDU/cords shortly so no adapter should be needed, assuming it's really a L6-30R on the provider end.

Disclaimer -- I never intended to break any codes, it was an oversight by me sending the wrong PDU, and onsite staff should have know better before hooking it up.

Plugging a 20A *PDU* into a 30A receptacle can be dangerous if

a) there is more than 20A of load plugged into it
b) it has no breaker, and
c) the cordset is only 12A, which is what you would expect on a 20A PDU.

-- jr 'up the voltage' a

Unless the device you are plugging in does not have its own breaker. If it doesn't, then your 20A cord could catch on fire before the 30A breaker trips. Not incredibly likely, but possible.


It's temporary unless it works.


Meh. It depends. Plug that 30 amp power strip into a 20 amp circuit.
Try to use more than 20 amps and the main breaker trips. No problem.

Plug that 20 amp power strip into a 30 amp circuit. Try to use more
than 20 amps and the strip's breaker trips. No problem.

Get a short before the strip breaker and the main breaker trips before
the wires can heat.

There just aren't a whole lot of failure modes here that result in
fire short of one or the other breaker failing. And that results in
fire regardless of the amperage mismatch.

This, by the way, is why you're allowed to plug that 22 gauge
Christmas light wire into a 15 amp receptacle even though it can't
handle 15 amps: the 3 amp fuse will blow if there's a short. Just
don't plug in anything with lower-rated wire that doesn't have its own
breaker or fuse.

Bill Herrin

And that is the result of the way things have been set down. The
electrical code (as well as just general common sense) requires that
there are multiple levels of protection specifically to try to avoid
"weird failure modes". So what we end up with is wire that is
overrated for the current it is supposed to carry, multiple fusable
links inbetween point A and point B and a grounding system that is
supposed to safely direct voltage away from people in the event that
everything else fails.

So back to what I said before, I don't like doing stuff like that and
don't advocate it if for no other reason that it makes good sense not
to put yourself into a potentially problematic situation.