question about train_elec.mains() for ukdale

[Hessen525]

Hi, Sir
Thanks for your help.
I am so confused for the following,

input(for ukdale):
train_meter = train_elec.submeters()['kettle']
train_mains = train_elec.mains()

output:
ElecMeter(instance=54, building=1, dataset='UK-DALE', site_meter, appliances=[Appliance(type='immersion heater', instance=1), Appliance(type='water pump', instance=1), Appliance(type='security alarm', instance=1), Appliance(type='fan', instance=2), Appliance(type='drill', instance=1), Appliance(type='laptop computer', instance=2)])
)

What is the meaning for this elecmeter ? is it site_meter for all application in this building ? but why there are part of application likes water pump, security alarm etc in the same ElecMeter.

Thanks,

[SphinxVG]

I have the same questions