nanog mailing list archives
Re: Reminder: Never connect a generator to home wiring without transfer switch
From: Jay Hennigan <jay () west net>
Date: Wed, 25 Aug 2021 11:11:11 -0700
On 8/25/21 10:25, Mel Beckman wrote:
Jay, No, because transformers work in both directions :)
I think you mean, "Yes, because transformers work in both directions." First of all, I absolutely agree that no one should attempt to energize their home wiring with a standby generator unless there is a proper transfer switch in place. I very much understand the safety concerns.
The question that Ethan raised makes sense, however. If power to several blocks is out and I connect my little 2KW Honda to my house wiring without a transfer switch, because transformers work in both directions my generator will see the load of the whole neighborhood. This will immediately and severely overload the generator and at best cause it to stall out or trip its output breaker, at worst to fail catastrophically.
In the very rare case that the outage is at the fuse on the pole pig feeding just my house or that of me and one or two neighbors, then indeed the generator may continue to run and that transformer will have distribution voltage of 4KV or so on the utility side, a very dangerous condition. That's a pretty unusual situation, however. Typical power outages are substantially more widespread. My little generator would be looking at the load of the entire outage area reflected through the (bidirectional as you note) transformers. The load of half the town will, as Ethan speculated, completely overwhelm any practical residential standby generator to the point that it stops producing power either by failure or by tripping its breaker.
Even if the generator were massive and survived, its branch circuit breaker or the house main would trip long before sufficient power to feed a large area was able to flow back into the utility's wiring.
Yes, connecting a generator without a transfer switch is a horrible idea and likely to get someone killed, agreed.* However, as the vast majority of power failures involve more than a single residence, the generator will fail to produce power immediately anyway due to looking at essentially a dead short.
* Every time I've seen utility workers working on lines that are assumed to be dead, the first thing they do is clamp them to ground to be certain. When the lines are assumed to be live, massive insulation sleeves, heavy gloves, insulated booms and the like are used.
-- Jay Hennigan - jay () west net Network Engineering - CCIE #7880 503 897-8550 - WB6RDV
Current thread:
- Re: Reminder: Never connect a generator to home wiring without transfer switch, (continued)
- Re: Reminder: Never connect a generator to home wiring without transfer switch Jay Hennigan (Aug 31)
- Re: Reminder: Never connect a generator to home wiring without transfer switch Mark Tinka (Aug 31)
- Re: Reminder: Never connect a generator to home wiring without transfer switch Sabri Berisha (Aug 31)
- Re: Reminder: Never connect a generator to home wiring without transfer switch Owen DeLong via NANOG (Aug 31)
- Re: Reminder: Never connect a generator to home wiring without transfer switch Warren Kumari (Aug 25)
- Re: Reminder: Never connect a generator to home wiring without transfer switch Jay Hennigan (Aug 25)
- Re: Reminder: Never connect a generator to home wiring without transfer switch Mel Beckman (Aug 25)
- Re: Reminder: Never connect a generator to home wiring without transfer switch Matt Erculiani (Aug 25)
- Re: Reminder: Never connect a generator to home wiring without transfer switch Amir Herzberg (Aug 25)
- Re: Reminder: Never connect a generator to home wiring without transfer switch Mel Beckman (Aug 25)
- Re: Reminder: Never connect a generator to home wiring without transfer switch Jay Hennigan (Aug 25)
- Re: Reminder: Never connect a generator to home wiring without transfer switch Michael Thomas (Aug 25)
- Message not available
- Re: Reminder: Never connect a generator to home wiring without transfer switch Jay Hennigan (Aug 25)
- Re: Reminder: Never connect a generator to home wiring without transfer switch Lady Benjamin Cannon of Glencoe, ASCE (Aug 30)
- Re: Reminder: Never connect a generator to home wiring without transfer switch Aaron C. de Bruyn via NANOG (Aug 30)
- Re: Reminder: Never connect a generator to home wiring without transfer switch Mel Beckman (Aug 30)
- Re: Reminder: Never connect a generator to home wiring without transfer switch Aaron C. de Bruyn via NANOG (Aug 30)
- Re: Reminder: Never connect a generator to home wiring without transfer switch Warren Kumari (Aug 30)
- Re: Reminder: Never connect a generator to home wiring without transfer switch Aaron C. de Bruyn via NANOG (Aug 30)
- Re: Reminder: Never connect a generator to home wiring without transfer switch Tom Beecher (Aug 30)
- Re: Reminder: Never connect a generator to home wiring without transfer switch Warren Kumari (Aug 30)