Electrical question I couldn't figure out
- Thread starter zappy
- Start date
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
CR3 is open. That's the only way there can be voltage across it. Closed contacts have no voltage across them.
Could you answer the rest?
Could you answer the rest?
Eddie702
Licensed Electrician
- Location
- Western Massachusetts
- Occupation
- Electrician
120 volts with no load voltage will lek through the light bulb
Right I get it now. Thank you.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
The fact that there is 120v between B and C indicates that CR must be open, and that the rest of the contacts must be closed.
kwired
Electron manager
- Location
- NE Nebraska
Leak through to where?
If the contacts were semiconductor devices like SCR's then you might get enough leakage current to pass through them to light up an LED or even neon indicator lights, except in this case you also have the CR1 coil in parallel with the lamp and it will have low enough impedance to shunt enough of that current away from the lamp that it won't light in most cases.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
That was supposed to be CR3.
hbiss
EC, Westchester, New York NEC: 2014
- Location
- Hawthorne, New York NEC: 2014
- Occupation
- EC
Funny how many guys don't think to measure voltage across a set of contacts. That will tell you if the contacts are open, closed or there is a problem with them. For instance, a large voltage from the line to load side of contactor contacts will tell you that there is high resistance and likely the contacts are burned or on the way out.
-Hal
-Hal
ptonsparky
Tom
- Occupation
- EC - retired
Not even very large. Somewhere in the plus side of 100mv. That and side by side comparisons.
- Location
- Illinois
- Occupation
- retired electrician
Same with checking for blown fuses on a circuit that has a load.
LarryFine
Master Electrician Electric Contractor Richmond VA
- Location
- Henrico County, VA
- Occupation
- Electrical Contractor
Yes, or across breakers. These checks are your basic fall-of-potential tests.
juliocstrjn
New User
- Location
- Phoenix
- Occupation
- Facilities Maint
CR2 thru CR5 are shown as contacts on the drawing yet the questions describe them as "energized" not closed or open I don't love it but we know what they meant to ask I guess....
Strathead
Senior Member
- Location
- Ocala, Florida, USA
- Occupation
- Electrician/Estimator/Project Manager/Superintendent
Huh, I find several of the other questions more challenging than. How about the last one? I had to read it twice, before it downed on me. Also, I don't like the wording. "the most likely"... I can think of several things that can CAUSE the issue that means the relay isn't closed, by no one is the most likely IMO.
Strathead
Senior Member
- Location
- Ocala, Florida, USA
- Occupation
- Electrician/Estimator/Project Manager/Superintendent
How about 20. Unless I miss my mark, either the coil is burned out, or one of the wires is disconnected. I don't see how one is more likely than the other.
kwired
Electron manager
- Location
- NE Nebraska
CR2 thru CR5 are relays. The drawing shows contacts operated by said relays (they happen to all be NO contacts) Most of us would take "energizing the relay" to mean apply voltage, within rating, to the relay coil if there is no other specific information to mean otherwise. Those contacts are going to change state when that happens.
- Location
- Placerville, CA, USA
- Occupation
- Retired PV System Designer
How are you seeing all that detail in the OP's image? For me it is too blurry to read any of the text or the labels on the drawing.
macmikeman
Senior Member
- Location
- Planet macmikeman
Cmon, I check voltage across crummy 15 amp residential grade light switches all the time as well, it's a good way to see if the filament is the issue.......
macmikeman
Senior Member
- Location
- Planet macmikeman
You not the only one..........
kwired
Electron manager
- Location
- NE Nebraska
My vision isn't great, but I could read the labels without glasses and without increasing display magnification.
I can't quite read the "load" element label in there though. The coils that go with the CR contacts are not in the drawing but won't effect the answers to the questions at the top.