Switch is switch

Question

The issue concerns 2 bedrooms that operate on different switches, obviously, but have different results than expected.
The combinations are as follows:
          Switch A            Switch B            Light A         Light B
1:              off                        off                      off                  off
2:             on                        off                      on                  on (dim)
3:             off                        on                      off                  on
4:             on (1st)               on (2nd)            on                  on (turns 
                                                                                          OFF light A)
5:             on (2nd)             on (1st)               off                  on

Sorry, but this is the only way I can explain.
I think a little rewire is called for?

Ragards John.

James · Accepted Answer

Hi John. Has this always been like this or have you recently changed the light fittings?

Manhar · Answer

As a Electition I think someone has swapped the wires while installing switches so it ain’t a big job just wires needs to be swapped

Del · Answer

are they standard lights and switches? what happens if you remove  each light/led and perform switching sequence?

Rzgar · Answer

you have DALI system (Digital Addressable Lighting Interface)

Aurel · Answer

Hi John 
we can gladly arrange a visit free of charge to provide with a quote for the repair . 
We expect it to be something really minor 
Best wishes

Mike · Answer

It sounds worse than it probably is probably just one cable wrong just needs disconnecting and belling the cables out to see what does what

Ian · Answer

HI John, definitely sounds like a bad DIY installation.  there is no way the lights should interact (ie cause issues with another rooms lights.). You dont need a rewire but you do need someone who knows what they are doing.    Cant give an idea of what it would cost as its impossible to know what has been done wrong until it is investigated.   Regards Ian.

Christopher · Answer

No rewire needed John, my guess is that the switch wires and loop have been crossed over somewhere. Very common diy mistake. 
Any electrical needs you may have:

Anthony · Answer

Yes  probably wired incorrectly probably sorted in under an hour

Peter · Answer

Hello John, you’ve actually explained this perfectly. Your "truth table" reveals a classic (and dangerous) wiring error often made during DIY renovations or by an inexperienced hand.You don't just need a "little rewire"—you have what is known as a Series Circuit cross-connection between two rooms. Currently, your two bedrooms are accidentally sharing a single neutral or live return path.What is happening? (The "Dim Light" Mystery)In Scenario 2, when Light B glows "dim," it’s because the electricity is flowing through Light A, then through Light B, and finally to the neutral.Using the formula for power $P = \frac{V^2}{R}$, because the two bulbs are in series, the voltage ($230V$) is being split between them. Neither bulb gets the full voltage they need to shine at full brightness, which is why they appear dim and "phantom-like."The Diagnosis: The "Stray" Neutral or LiveThe most likely culprit is a shared neutral or a cross-wired switch feed in a junction box (likely under the floorboards or in the loft between the two rooms).The Fault: Switch A is likely "feeding" Switch B. When you turn on Switch A, the power travels into the circuit for Room B.The Result: This creates a loop where one light depends on the other to complete the circuit. This is why in Scenario 4 & 5, turning one switch on actually kills the other light—you are creating a "dead end" or a path of least resistance that bypasses the first bulb.Why this is a Priority FixThis isn't just a nuisance; it's a fire and safety hazard for two reasons:Overloading: You may be pulling more current through a single thin cable than it was designed to carry.Borrowed Neutrals: If an electrician works on Bedroom A and turns off the fuse, the wire could still be "live" because it’s getting back-fed from Bedroom B. This leads to electric shocks.What to do nextBecause this involves tracing a fault across two different circuits/rooms, I strongly recommend calling a Part P registered electrician.What to tell them:"I have a 'shared neutral' or 'series circuit' fault between two bedrooms. When Switch A is on, Light B glows dimly, and the switches are interacting with each other's loads."What they will do:They will use a continuity tester to find where the two circuits are touching.They will likely look in the ceiling rose of the first bedroom or a junction box in the loft.They will separate the "switch lives" so each room has its own independent path to the consumer unit.Would you like me to help

Switch is switch

Follow Us

Cookies

Manage Cookies

Essential cookies

Analytics & Tracking

Advertising