My favorite airbnb host has an electrical problem...brownouts.

Status
Not open for further replies.
J

jdaddy29

Member
Location
Augusta, GA
Occupation
Electrical engineer (DC/Automotive)
Hi guys, new here. I may have already learned more in the few threads I've read here than in any of my undergrad classes... thank you for that!

I have a favorite Airbnb unit I stay in when I travel for work. But he's got some serious electrical issues going on-- namely, severe voltage sag (i like "brownouts" although maybe not technically accurate) under heavy load.

My first thought was a bad neutral on the service line, but I decided to investigate more. Here's the story:

Set up:
Rental unit is on a sub panel and the lines are buried from the meter to the subpanel. 65A worth of breakers reside in the sub. Unit has all electric service: mini-split HVAC, electric hot water, and no fewer than 3 motors on the well (I think there's a reverse osmosis filtration system in place). Actually the well pumps may or may not be on the sub, since I couldn't trace their wiring to the source.

Symptom:
Whenever the HVAC and water heater are running simultaneously, the lights and fans dim dramatically inside the unit. I measured voltage as low as 109.0 VAC at a receptacle during these events. No breakers ever tripped at any point during my stays. On the second night, the transformer at the street blew up, resulting in a street-wide service outage lasting overnight. Maybe coincidence? Whatever the case, the unit's problems persisted after electrical service was restored.

Investigation:
Caveats: I only had access to the unit sub panel. The meter box was locked and the service lines were fully enclosed in conduit up the 20ft pole. The breaker box was inaccessible as the main house was locked. The lines to the sub appeared to be coming off the meter/pole rather than from the house.
I'm attaching a few photos from the sub. It looks to me like the owner ran a single leg of 120 to the unit sub; I didn't measure 240 anywhere inside the sub. I confirmed the water heater was 120, can't remember explicitly checking the HVAC. Only 3 wires though... guess that's not definitive.
Again, frequent brownouts at the unit with low voltage readings of 109 during.

Many photos here. I hope it's okay to post this way....couldn't find an add photo button:

https://drive.google.com/drive/folders/10evW_kr6Sh7hb1mVz-qi_yjzcjiU2DTP

Conclusive, or additional information needed?
I've read on this forum about the importance of load balancing. If he's pulling the whole unit load from one leg of 120, about 65A, does that constitute a serious imbalance? Would that explain the voltage sag? Does this appear to be the case from the photos of the sub panel?
Can I draw any conclusions at this point or is it still ambiguous based on limited information gathered?
How great is the danger to life, limb, or property in this case?

Thanks for your advice, y'all! I'm not making any money in this, BTW, it's purely a learning/curiosity thing for me at this point.
 
If it were a bad neutral, the voltage on one leg would increase as the other decreases with large single phase loads. Since lights dim when 240V loads come on, that’s not likely the problem.
It’s more likely that something in the service is undersized, such as the utility transformer or service entrance conductors. It’s hard to say much more than that.
The situation is likely not dangerous, but could be detrimental to any loads adversely affected by under voltage.
 
Looking your first photo it looks to be a 3 circuit 120V panel to the guest suite (Air bnb), I cant make out the feeder wire size but looks to be a #10. The jumper to the other lug could be the issue. For some reason it appears the red is being used as a neutral.
There are many code violations in that panel, along with the ductless and the well pump.panel-s.jpg
 
retirede said:
If it were a bad neutral, the voltage on one leg would increase as the other decreases with large single phase loads. Since lights dim when 240V loads come on, that’s not likely the problem.
It’s more likely that something in the service is undersized, such as the utility transformer or service entrance conductors. It’s hard to say much more than that.
The situation is likely not dangerous, but could be detrimental to any loads adversely affected by under voltage.
Click to expand...
There are no 240 loads in the unit.
 
jdaddy29 said:
There are no 240 loads in the unit.
Click to expand...
With 240 volt loads dimming the lights, aggravated by small feeder to the unit. Probably either too small poco transformer with multiple houses, or long feed from the transformer with small wire. Another possibility is burnt contacts in the main breaker. A FOP test can easily check that.
 
Homeowner wiring. Code violations are like potato chips, you never eat just one.

Walk away or run, especially if you have a license on it. Do not touch it.

If you want to stay there again, bring your own battery backup line conditioner, plus flashlights and charged batteries. Bring a line conditioner unit that works just fine on 90 V. If you want to look at it, an IR scan would be indicated.
 
What you need to tell your fav Airbnb owner is that what he has there is not just untidy, but plain wrong, contains multiple code violations just in that photo, and possibly dangerous and that he needs to hire an electrician to sort the whole thing out.
 
A few solutions avoiding the root of the problem, although not always practical:
- soft start for air conditioner
- better LED drivers that can handle wild voltage drops and other line noise
- an always online UPS (not in bypass or "ECO" mode) or line conditioner that tolerates 90V (this is a super normal spec in Japan). Any decent UPS will have a boost transformer that can handle that sag. You could also put your own buck boost transformer before a UPS. In most situations, provided it is within the specifications of the UPS manufacturer, you are better off providing the UPS with 140 rather than 90V, as in extreme conditions the voltage will drop even lower.

Off topic, but this reminds me of when we get single phased delta services (e.g. one of the three medium voltage conductors is lost or fuse blown) in South America - the voltage drops from 220 to ~130V on the two other wye phases. On those other ghost phases (or parts of the single phase "circuit," I suppose I should say), LED drivers, computers and switch mode power supplies like phone chargers continue to work because of their wide voltage tolerance range. Some UPSs with a wide voltage range input are even still happy. The elevator VFDs and air conditioners always shut down though.
 
Last edited:
ruxton.stanislaw said:
A few solutions, although not always practical:
- soft start for air conditioner
- better LED drivers that can handle wild voltage drops and other line noise
- an always online UPS (not in bypass or "ECO" mode) or line conditioner that tolerates 90V (this is a super normal spec in Japan). Any decent UPS will have a boost transformer that can handle that sag. You could also put your own buck boost transformer before a UPS. In most situations, provided it is within the specifications of the UPS manufacturer, you are better off providing the UPS with 140 rather than 90V, as in extreme conditions the voltage will drop even lower.

Off topic, but this reminds me of when we get single phased delta services (e.g. one of the three medium voltage conductors is lost or fuse blown) in South America - the voltage drops from 220 to ~130V on the two other wye phases. On those other ghost phases (or parts of the single phase "circuit," I suppose I should say), LED drivers, computers and switch mode power supplies like phone chargers continue to work because of their wide voltage range of voltage tolerance. Some UPSs with a wide voltage range input are even still happy. The elevator VFDs and air conditioners always shut down though.
Click to expand...
That was interesting, thanks for sharing!
 
tthh said:
What you need to tell your fav Airbnb owner is that what he has there is not just untidy, but plain wrong, contains multiple code violations just in that photo, and possibly dangerous and that he needs to hire an electrician to sort the whole thing out.
Click to expand...
That is the best advice that can be given.
 
Since this is a rental property, it should be condemned until the owner makes the necessary repairs. No way should anybody be allowed to stay there while he collects money for it!

There is NOTHING there that can be salvaged. Looks like the owner has a long history of illegal DIY electrical work.

-Hal
 
I think this is where we need to put this to bed. The best advice was given in post #11.
 
Status
Not open for further replies.
Top