PLC/Relay interlocking scheme - Shorebrook PE Exam Question 54

[akyip]

Hey guys,

I just want to confirm this regarding a PLC/relay interlocking scheme question from Shorebrook PE Power Exam, question 54.

Shouldn't the solution to this problem actually be D? At least, that's how I learned it from Zach Stone's Electrical PE Review class.

If you use the given solution C :

• When you press the PB-A push button, this de-energizes Relay Coil RA and light LX, since it opens the normally closed contact RA leading to these two.
  
• When you press the PB-B push button, this de-energizes Relay Coil RB and light LY, since it opens the normally closed contact RB leading to these two.
  

I just want to confirm that the solution to this problem should actually be D.

Thanks for any input on this!

 

[Orchid PE]

I agree the answer should be D.