Never use door bell wire for the layout!
Use copper wire 21-22 AWG for the digital system with 3 amp.
Recommended is to not solder the wires.
Use contact clips.

Hello Goofy
can i ask you what wire you prefer for lighting (layout leds, buildings, using DC) ?
mean thicker than 21-22 AWG or the same
thank you in advance
Harris

The wire should be thick enough to handle the output current of the booster. The internal booster of the z21 is rated for 3 A.
20 AWG is 0.519 mm² in metric units and should be safe with 3 A IMHO, even though this chart only shows 1.5 A for power transmission:
https://www.powerstream.com/Wire_Size.htm

The length of the wires matters. If wires are too thin and too long, a short circuit may not trigger the overload protection which can lead to melting down a loco or burning down the house.
Using a long speaker cable for power distribution and only short pieces of the bell wire to feed the tracks could improve the safety of the installation.

20 AWG is thicker than the 21 or 22 AWG you recommend.

Bell wire sounds like 24 AWG or thinner in my ears. Such thin wire should not be used for digital layouts with boosters rated for 3+ A.

Obviously this is not a "open and shut case". Due to the fact that my layout is simple and will not change I think I agree with the post "its fine". I loved the links. Thanks. Very informative. I agree that 20AWG solid can handle 3A peaks without burning, it is deceptively thinner than the small amount of 20AWG flexible wire I have on hand. Mostly I learned that solid wire can do the same thing as stranded, it's just not flexible and can work harden and break. Some responses have more to do with convenience and use than just "will it work". But I got great ideas from you all that helped me decide what to do.

Using wire I have on hand I will run a 10' length of lamp cord/speaker wire as a power distribution bus down the center of the layout. I have just enough 20AWG multi strand from my RC flying hobby supplies to connect to the track at four points from this. I always planned to solder the wires to the track, soldering is the single best way to save money in this hobby IMHO ;) I'll return the spool of bell wire to the hardware store and get my $14 back.
I think I should adopt the Marklin standard going forward in this hobby, any standard would be fine, so why not Marklin, and stock up on wire spools. That way I'll always have color coded wire to use with speaker bus wire. Thanks!