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Electrical question I couldn't figure out

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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?
 

kwired

Electron manager
Location
NE Nebraska
Occupation
EC
120 volts with no load voltage will lek through the light bulb
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.
 

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
 
Location
NE (9.06 miles @5.9 Degrees from Winged Horses)
Occupation
EC - retired
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
Not even very large. Somewhere in the plus side of 100mv. That and side by side comparisons.
 

don_resqcapt19

Moderator
Staff member
Location
Illinois
Occupation
retired electrician
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
Same with checking for blown fuses on a circuit that has a load.
 

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
Occupation
EC
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....
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.
 

kwired

Electron manager
Location
NE Nebraska
Occupation
EC
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.
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.
 
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