voltage between phase a & b changes

[efxdad1]

i have a single phase system
day 1
i check voltage it is 122v to ground on phase a
same on phase b
but no 240v between phases
day 2 the 240v comes back between phases
day 3 the 240 voltage is gone but the 122v from phase a&b to ground is there
this has happened 3 times
how is this happening
confused
thanks
my email {has been removed by a moderator}

 

[charlie b]

A little more information would help. Sample questions I might ask:

1. Is this a service panel, or is it downstream of a step down transformer, or downstream of a distribution panel?
2. Am I right in inferring that it is rated 120/240 volts?
3. Where exactly are you takikng the voltage measurements?
4. What type of meter are you using?
5. Do you check that the meter is working properly, by checking some other known voltage source before and after you take the readings?
6. Do you stop by this location once a day to take measurements, and do you just take one set of measurements and leave, or do you check several times each day?
7. Is anything large being turned on or off, while you are there, or between your visits?
8. What type of facility is this?
9. Is this a new installation, or an old installation with new problems?

That's enough for now. Any additional info would help. Welcome to the forum.