Do Not Disconnect Under Load!

[derekleffew]

This is a Question of the Day. Students-Only are permitted to reply, until after 01/18/24, when it will be open to everyone.

Saw a picture on Ye Olde ControlBooth of which I'd never seen:

It's the back of a ETC Sensor SP620 with Socapex and 2P&G outputs. Both of the Socapex outlets have "DO NOT DISCONNECT UNDER LOAD!" warnings.

So I have some questions...
1. Is this s new thing? The pack is at least one generation old.
2. Is it a code thing? If yes, shouldn't the title be stated so we can find more info?
3. Why only unplugging and not plugging in prohibited?
4. I likely missed something, so make up your own (relevant!) question and answer it.

 

[gafftapegreenia]

Just here to comment on the lack on strain relief on that 2P&G

 

[TimMc]

This is a Question of the Day. Students-Only are permitted to reply, until after 01/18/24, when it will be open to everyone.

Saw a picture on Ye Olde ControlBooth of which I'd never seen:

It's the back of a ETC Sensor SP620 with Socapex and 2P&G outputs. Both of the Socapex outlets have "DO NOT DISCONNECT UNDER LOAD!" warnings.

So I have some questions...
1. Is this s new thing? The pack is at least one generation old.
2. Is it a code thing? If yes, shouldn't the title be stated so we can find more info?
3. Why only unplugging and not plugging in prohibited?
4. I likely missed something, so make up your own (relevant!) question and answer it.

Ooop... Missed the students only.

 

[derekleffew]

So I have some questions...
1. Is this s new thing? The pack is at least one generation old.
2. Is it a code thing? If yes, shouldn't the title be stated so we can find more info?
3. Why only unplugging and not plugging in prohibited?
4. I likely missed something, so make up your own (relevant!) question and answer it.

One from the peanut gallery:
5. Does the prohibition apply to all Socapex connectors or just these mounted on this dimmer pack?
6. Does it apply to one circuit, random circuits, or all six circuits of the multi-cable?

 

[JonCarter]

(Where are all our students??) Anyway, Ideally one should neither connect nor disconnect things under load. Disconnecting under load will result in an arc between the parting terminals and (in the case of these mini-pins such as socapex) possibly damage them seriously, depending on the load, possibly to the point of requiring replacement of the connector. As far as connecting under load, usually there will be some arcing, the seriousness of which depends on the load and how positively the connection is made. (And if you're disconnecting a DC circuit under load, you'll have a nice unintended arc lamp running as you do it.)
To your additional questions:

1. Is this s new thing? The pack is at least one generation old.

No, it's been common knowledge and common sense for years.

2. Is it a code thing? If yes, shouldn't the title be stated so we can find more info?

I don't know if it's a "code thing" or not, but it's a common sense thing.

3. Why only unplugging and not plugging in prohibited?

The writer of the label didn't go far enough?

4. I likely missed something, so make up your own (relevant!) question and answer it.

 

[MNicolai]

The writer of the label didn't go far enough?

It's because maintaining an arc over an air gap is easier than sparking one initially. 120/208V simply isn't a high enough voltage to reach out and grab a potential load path through the air -- but when you disconnect under load, an arc is maintained over a longer duration and air gap distance, scorching the terminals with carbon build-up along the way. Over time, this carbon build-up on terminals creates more electrical resistance at the surface of the terminals which translates to more heat when under load, and leads to a greater likelihood of the connector melting down.

Which is to say -- disconnecting 20A/120V under load once is not likely to be destructive, but doing it repeatedly will generate more carbon build-up, more heat, and will increase the likelihood of a catastrophic failure.

Certain designs of connectors and terminals are more resilient to this effect. Others are not. 2P&G connectors for example, have a lot of conductive surface area so a little carbon build-up on the ends of the connectors will be less destructive given that once the connectors are fully mated, there is plenty of "clean" conductive surface area left. Original PowerCon connectors had much less resilient designs where the risks of arcing and heat from disconnecting under load were much more likely to create a problem.

As for it being a code thing -- not to my knowledge. It's more of a listing thing. Connectors can be listed by an NRTL (such as UL, ETL, etc.), after laboratory testing for safety and destructive testing, as being safe for breaking under load or not. Some designs of connectors do not pass this test because they are inherently susceptible to arcing upon disconnect either jumping between contacts or creating enough carbon buildup and heat that they will damage those connectors.

 

[TimMc]

Connectors can be listed by an NRTL

Nationally Recognized Testing Laboratory?

 

[avkid]

Nationally Recognized Testing Laboratory?

Yes,
OSHA NRTLs

 

[derekleffew]

I'm still curious as to why the "Labelers" decided to call out "breaking" but not "making" under load. I wonder if there is someone at ETC who could answer this? By prohibiting one act but not the other, aren't they ...searching for word...tacitly?... approving the unmentioned?

I undertand the science, but with 2P&G connectors, I've always gotten a larger/louder spark when plugging rather than unplugging. Or at least I thought I had.

 

[JonCarter]

There are devices made for making & breaking circuits under load. They're called SWITCHES., not "connectors."

Isn't there something we're supposed to have learned w--a--a--a--y back, maybe when 5 yrs. old: Use the correct tool for the job.

 

[FMEng]

I'm still curious as to why the "Labelers" decided to call out "breaking" but not "making" under load. I wonder if there is someone at ETC who could answer this? By prohibiting one act but not the other, aren't they ...searching for word...tacitly?... approving the unmentioned?

I undertand the science, but with 2P&G connectors, I've always gotten a larger/louder spark when plugging rather than unplugging. Or at least I thought I had.

Plugging in with power applied is much worse than unplugging because cold lamp filaments have much lower resistance than hot ones. That initial current is called "inrush" and it can be several times the normal current, for a split second. The short duration is why inrush doesn't cause circuit overloads.

 

[danTt]

I agree that "Making" a soca under load has much more audible arcing than "Breaking" one, and has certainly burned out connectors for me in the past (Same with powercon). I'm not sure why this specifically calls out breaking and not making, but I'm curious to know more as well.

I can't tell in the picture @derekleffew , is the same warning reproduced in the fine print above the cams? Or are they "fine" to disconnect under load according to the pack?

 

[jtweigandt]

Since it's in writing... you might say there's an Arc in that Covenant...
(ducking for cover)

 

[danTt]

To add a related question-- does the fact that some socapex connectors have a metal shell/metal locking ring play into this warning at all? I've yet to see metal camlock connectors for some reason...

 

[brucek]

Tangledly related is that PowerCon are NOT rated to rupture under load....but True1 ARE.

 

[MNicolai]

I agree that "Making" a soca under load has much more audible arcing than "Breaking" one, and has certainly burned out connectors for me in the past (Same with powercon). I'm not sure why this specifically calls out breaking and not making, but I'm curious to know more as well.

I can't tell in the picture @derekleffew , is the same warning reproduced in the fine print above the cams? Or are they "fine" to disconnect under load according to the pack?

When you look at the slo-mo of an electrical arc over an air gap, the arc jumps to ground by putting out "feelers" that stray in different directions as the source voltage finds the lowest path of resistance through the air. The difference in audible noise between mating versus unmating could be as simple as as when you are disconnecting, the arc effectively has its path through the air gap already established like surfing in the wake of a boat. That initial arc as you are mating the connector though may be superheating a larger volume of air as these feelers network their way through the air in search of that path of least resistance between the source voltage and the ground path through that air gap.

Important to note that the IEC standard for breaking capacity that's cited for True1 connectors doesn't distinguish mating from unmating. The validation test for CBC "Circuit Breaking Capacity", at least from an older version of the standard I was able to dig up, simply mates/unmates the connector many cycles and an inspection for damage is made. There is no unique assessment of damage from mating under load versus unmating. I've dug around a little bit and many sources suggest disconnection under load is worse than mating under load, but I haven't found any empirical data or scientific explanation one way or another. I would not be surprised though if the audible noise of one versus the other are not directly correlated with proportion of wear on the connectors.

For additional reference: LEX Products' technical info.

 

[derekleffew]

As usual, @STEVETERRY enlightens:

First of all, it is the connector manufacturers that elect to list their product as an "appliance coupler" (such as the popular Neutrik PowerCon). They do so because the design of the contacts cannot pass the UL "break under load" test. The arc created during the break is more damaging to the contacts than the one created during a make. Updated connectors such as the Neutrik True1 TOP are rated for make and break under load. However, those connectors are still listed as appliance couplers. Therefore, they are not general-purpose connectors suitable for field attachment to building wiring. They must be used inside a listed product or wiring device enclosure that includes terminals for field wiring if they are to be directly connected to building wiring.

ST

It almost seems like ETC is the "victim" here. Because they use a popular (though not fully-vested) connector on their dimmer rack, they must post a warning label. Two in this case. Does every piece of equipment need such a warning "Hold on, I'm not done reading this PARbar yet..."