Reminder: Never connect a generator to home wiring without transfer switch

Jay Hennigan jay at
Mon Aug 30 18:25:56 UTC 2021

On 8/30/21 10:46, Aaron C. de Bruyn via NANOG wrote:

> While they were waiting for a few more trucks to arrive with a 
> replacement pole, I got to ask them a few questions.  They said it's 
> standard practice for them to ground on both sides exactly for the 
> reason that someone might accidentally connect a generator.  They open 
> the nearest switch on the upstream side, test to make sure the line is 
> dead, install grounds on all the wires, then test the downstream side 
> and attach grounds to all the wires, effectively making the work zone an 
> isolated segment.

I don't think anyone participating in this forum was remotely close to 
suggesting that anyone connect a generator to home wiring without a 
transfer switch in place. It's stupid and dangerous.

The point that several brought up is that doing so is not only a bad 
idea, but that it simply won't work in the vast majority of power outage 
scenarios. Unless the outage is on your service drop or on your pole 
pig, the impedance of the neighborhood or city downstream of the outage 
as reflected through the transformers will vastly overwhelm any portable 
generator capable of being connected with a "suicide cord" by several 
orders of magnitude.

The other point is that, assuming that the utility is following their 
safety protocols, the utility worker is going to ground the load side as 
well as the incoming feed specifically to prevent backfeeding the grid 
from a miswired generator.

Yes, never connect a generator to home wiring without a properly 
installed transfer switch.

Yes, the utility workers should ground the load side to avoid being 
killed in the event that someone does so.

Yes, if the utility follows all procedures correctly, and you happen to 
connect your miswired generator at the exact instant that the utility 
worker removes the ground after making the connection, and said worker 
grabs the conductor with bare hands, and there's a path to ground 
through the worker's body at that instant, that worker is probably going 
to die. The probability of this happening is somewhat greater than that 
of winning the lottery, but if they're on a pole in the middle of a 
storm working on overhead wires, the odds of their being struck by 
lightning are also worth considering.

It's a warning worth repeating, but probably not to this extent.

>     This is NANOG -- I'm sure that we've all followed a set of steps
>     perfectly and still managed to redistribute BGP into the IGP, or
>     apply an ACL and lock ourselves out of a box, or types "show run"
>     and watched the router randomly reboot. 

Don't forget the classic "switchport trunk allowed vlan" vs. "switchport 
trunk allowed vlan add".

Jay Hennigan - jay at
Network Engineering - CCIE #7880
503 897-8550 - WB6RDV

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