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Computer, monitor and modem? If you only have 3 devices connected, you may ask the electrician if he could install a 3 gang socket, They are available. Most likely he can get one, or he has one on him. If he calls you for an appointment, I would inform him of your needs so he can come prepared. The fire issue isn't the wall plug, it's the cord from the wall plug to the 4 way. Friction, chafing....that's the issue with extensions, and the landlord doesn't want any increases in insurance on his property.